Methods of forming a superhard structure or body comprising a body of polycrystalline diamond containing material

ABSTRACT

A method of producing a free standing PCD comprises forming a mass of combined diamond particles and precursor compound(s) for the metals of the metallic network by suspending the diamond particles in a liquid, and crystallising and/or precipitating the precursor compounds in the liquid. The mass is then removed from suspension by sedimentation and/or evaporation to form a dry powder of combined diamond particles and precursor compound(s). The powder is subjected to a heat treatment to dissociate and reduce the precursor compound(s) to form metal particles smaller in size than the diamond particles to provide a homogeneous mass. This is then consolidated using isostatic compaction to form a homogeneous cohesive green body of a pre-selected size and 3-dimensional shape. The green body is subjected to high pressure and high temperature conditions such that the metallic material wholly or in part becomes molten and facilitates diamond particle to particle bonding via partial diamond re-crystallisation to form a free standing PCD body.

FIELD

This disclosure relates to methods of making a superhard structure orbody comprising a body of polycrystalline diamond containing materialand a body made by such methods.

BACKGROUND

Polycrystalline diamond materials (PCD) as considered in this disclosureconsist of an intergrown network of diamond grains with aninterpenetrating metallic network. This is illustrated schematically inFIG. 1 which shows the microstructure of PCD material comprising theintergrown network of diamond grains 1 with an inter-penetratingmetallic network 2 with facets occurring at the diamond-metal interfaces3. Each grain has a degree of plastic deformation 4. Newly crystallizeddiamond bonds 5 bond the diamond grains as shown in the inset of thisfigure. The network of diamond grains is formed by sintering of diamondpowders facilitated by molten metal catalyst/solvent for carbon atelevated pressures and temperatures. The diamond powders may have amonomodal size distribution whereby there is a single maximum in theparticle number or mass size distribution, which leads to a monomodalgrain size distribution in the diamond network. Alternatively, thediamond powders may have a multimodal size distribution where there aretwo or more maxima in the particle number or mass size distribution,which leads to a multimodal grain size distribution in the diamondnetwork. Typical pressures used in this process are in the range ofaround 4 to 7 GPa but higher pressures up to 10 GPa or more are alsopractically accessible and can be used. The temperatures employed areabove the melting point at such pressures of the metals. The metallicnetwork is the result of the molten metal freezing on return to normalroom conditions and will inevitably be a high carbon content alloy. Inprinciple, any molten metal solvent for carbon which can enable diamondcrystallization at such conditions may be employed. The transitionmetals of the periodic table and their alloys may be included in suchmetals.

Conventionally, the predominant custom and practice in the prior art isto use the binder metal of hard metal substrates caused to infiltrateinto a mass of diamond powder, after melting of such binders at theelevated temperature and pressure. This is infiltration of molten metalat the macroscopic scale of the conventional PCD construction, i.e.,infiltrating at the scale of millimeters. By far the most commonsituation in the prior art is the use of tungsten carbide, with cobaltmetal binders as the hard metal substrate. This inevitably results inthe hard metal substrate being bonded in-situ to the resultant PCD.Successful commercial exploitation of PCD materials to date has beenvery heavily dominated by such custom and practice.

For the purposes of this disclosure, PCD constructs which use hard metalsubstrates as a source of the molten metal sintering agent viadirectional infiltration and the bonding in-situ to that substrate, arereferred to as “conventional PCD” constructions or bodies. This isillustrated in FIG. 2 which is a schematic diagram of the infiltrationprocess in a conventional PCD body with arrows indicating the directionand the long range of the infiltration through 2 to 3 mm of thickness ofthe PCD layer. The arrows in the inset 11 indicate again that the rangeof infiltration transcends many diamond grains. The PCD layer 6 in aconventional PCD body is normally of the order of 2 to 3 mm inthickness. The substrate 7 is predominantly made of tungstencarbide/cobalt alloy. The number 8 indicates approximately the directionof the infiltration of the cobalt infiltrant through the thickness ofthe PCD layer during the high pressure high temperature process. Theoval region 11 is at the interface between the carbide substrate and thePCD layer, and the inset of FIG. 2 shows schematically an expanded viewof region 11 with the diamond grains in this region through which thelong range infiltration of cobalt occurs. The inset highlights the factthat the directional infiltration transcends many grains through thethickness of the PCD layer. The diamond grains 9 and 10 may typically beof varying size in the body and could be made of multi modal mixes ofdiamond particles.

It has been appreciated that this conventional approach to themanufacture of PCD bodies results in a series of limitations andconstraints which in turn have undesirable consequences in manyapplications. These limitations include:

-   -   1. Macroscopic residual stress distributions (at the scale of        the conventional PCD body i.e. at the scale of millimeters) in        the PCD body which inevitably have deleterious tensile        components.    -   2. A dimensional limitation of PCD material layers in the        direction of the infiltration of the molten metal from the        substrate.    -   3. Structural and compositional in-homogeneities as a result of        directional molten metal infiltration over a distance of the        order of millimeters.    -   4. Significant practical difficulties in exploiting a broad        range of metal alloy compositions and limited metallurgical        compositions which result there from.    -   5. Micro residual stress management at the scale of the diamond        micro structural grain size is limited and impractical.    -   6. Manufacturing degrees of freedom such as grain size        distribution, metal content and metal alloy composition are        co-dependent and cannot readily be independently preselected,        chosen or varied.

The present applicants have appreciated that the limitations andproblems with respect to homogeneity, macroscopic and microscopicresidual stresses, size and shape of the PCD body, and restricted choiceof material composition described above for conventional PCD bodies orconstructions give rise to poor or inadequate performance in manyapplications.

There is a need for the development PCD bodies of any 3-dimensionalshape, with high material homogeneity and with the absence ofmacroscopic residual stress, and with an expanded choice of PCD materialstructure and composition, with attendant micro residual stress control,all of which are highly desirable.

SUMMARY

-   -   1. Viewed from a first aspect there is provided a method of        producing a free standing PCD body comprising a combination of        intergrown diamond grains forming a diamond network and an        interpenetrating metallic network, not attached to a second body        or substrate made of a different material such as a metal,        cermet or ceramic, the method comprising the steps of:        -   a. forming a mass of combined diamond particles and            precursor compound(s) for the metals of the metallic network            by suspending the diamond particles in a liquid, and            crystallising and/or precipitating the precursor compounds            in the liquid;        -   b. removing the mass from suspension by sedimentation and/or            evaporation to form a dry powder of combined diamond            particles and precursor compound(s);        -   c. subjecting the powder to a heat treatment to dissociate            and reduce the precursor compound(s) to form metal particles            smaller in size than the diamond particles to provide a            homogeneous mass;        -   d. consolidating the homogeneous mass of diamond particles            and metallic material using isostatic compaction to form a            homogeneous cohesive green body of a pre-selected size and            3-dimensional shape; and        -   e. subjecting the green body to high pressure and high            temperature conditions such that the metallic material            wholly or in part becomes molten and facilitates diamond            particle to particle bonding via partial diamond            re-crystallisation to form a free standing PCD body;            wherein:            -   the diamond network of the PCD body is formed of diamond                grains having a plurality of grain sizes, the diamond                network comprising a grain size distribution having an                average diamond grain size, wherein the largest                component of the diamond grain size distribution is no                greater than three times the average diamond grain size;                and            -   the PCD material forming the free standing PCD body is                homogeneous, the PCD body being spatially constant and                invariant with respect to diamond network to metallic                network volume ratio, wherein the homogeneity is                measured at a scale greater than ten times the average                grain size and spans the dimension of the PCD body, the                PCD material being macroscopically residual stress free                at said scale.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments will now be described by way of example and with referenceto the accompanying drawings in which:

FIG. 1 is schematic diagram of the microstructure of PCD materialshowing the intergrown network of diamond grains with aninter-penetrating metallic network with facets occurring at thediamond-metal interfaces;

FIG. 2 is a schematic diagram of the infiltration process in aconventional PCD body with arrows indicating the direction and the longrange of the infiltration through 2 to 3 mm of thickness of the PCDlayer;

FIG. 3 is a schematic diagram of the very localised or short rangemovement of metal during the sintering of diamond particles to form anembodiment of PCD showing the diamond particles with well andhomogeneously distributed, smaller metal particles;

FIG. 4 is a graph of cobalt content versus average grain size of thestarting diamond particles for PCD sintered by the conventional route;

FIG. 5 is a generalized flow diagram showing two alternative approachesof embodiments of the method and preferences, laid out in two columns,for combining diamond powders with appropriate metals to form a mass ofparticulate material, which after forming into a 3-dimensionalsemi-dense body is subjected to high temperature and pressure conditionsto melt or partially melt the metal and partially re-crystallize thediamond to create the free standing PCD body;

FIG. 6 is a schematic diagram for the method of FIG. 5 column 2;

FIG. 7 is a cobalt, carbon binary phase diagram;

FIG. 8 is a schematic representation of a diamond particle showing metalparticles decorating the surface;

FIGS. 9 a and 9 b are SEM micrographs of whisker-like crystals of cobaltcarbonate decorating the surfaces of 2 micro meter sized diamondparticles;

FIGS. 10 a and 10 b are SEM micrographs of cobalt metal particlesdecorating the surfaces of 4 micro meter sized diamond particles;

FIG. 11 is a TEM micrograph of a diamond particle decorated in cobaltmetal particles together with a schematic diagram of the diamondsurface;

FIG. 12 is two SEM micrographs of diamond particles decorated in cobaltparticles and tungsten carbide;

FIG. 13 is an SEM micrograph showing a multimodal size distribution ofdiamond particles which have been co-decorated in cobalt and tantalumcarbide particles;

FIG. 14 is an embodiment of a 3-dimensional shaped PCD body intended foruse in general applications;

FIG. 15 is an SEM micrograph of mixed cobalt nickel carbonate crystalsdecorating 1 micron diamond particles; and

FIG. 16 is an SEM micrograph showing 95% cobalt, 5% nickel alloy metalparticles decorating the surfaces of 1 micron diamond particles.

DETAILED DESCRIPTION

Prior art methods for making PCD materials are dominated by the use ofsubstrates of metallic materials which provide a source of molten metalsolvents for carbon which are caused to infiltrate a mass of diamondparticles and via partial diamond recrystallisation result in diamondparticle to particle intergrowth or sintering. Inevitably, suchsubstrates are bonded to the resultant PCD material during suchmanufacturing procedure. There are many structural compositional anddimensional limitations and restrictions to the PCD material whichfollow from the use of such substrates. These include unavoidable macroresidual stress distributions, PCD material layer thicknesses restrictedpractically to about 3 mm or less and limitations in both diamond tometal ratio and the elemental and alloy composition of the metal. Thelimitations of these prior art constructions which have been appreciatedby the present applicants are set out below.

-   1. The residual stress is a distribution of tensile and compressive    stresses in the body of the PCD material. At the scale related to    the diamond grain size, which generally may be considered to be at    the scale of less than ten times the average diamond grains size,    where the coarsest component of grain size is no greater than three    times the average diamond grain size, the stresses operative may be    defined as and referred to as the “micro residual stress”.    -   At the scale greater than ten times the average diamond grain        size, where the coarsest component of diamond grain size is less        than three times the average diamond grain size, the stresses        operative may be defined as and referred to as the “macro        residual stress”. Typically, for very fine PCD grain sizes this        is at a scale greater than a few tens of micro meters. For        coarse grain sized PCD materials, this scale may typically be        greater than a tenth of a millimeter.    -   In the case of conventional PCD constructions the bonding of the        substrate to the PCD layer invariably results in a macro        residual stress distribution. This is as a result of the thermo        elastic mismatch between the materials of the PCD layer and the        substrate which, as a result of differential thermal contraction        and elastic expansion, causes the residual stress distribution        to form, on return to room temperature and pressure at the end        of the sintering process. In the general case of metallic        substrates, although the overall average macroscopic stress in        the PCD layer is compressive, the residual stress distribution        unavoidably, always has significant tensile stress components        due to bending effects of the bonded PCD body. These tensile        stress components promote crack propagation leading to early        fracture of the PCD body during general mechanical applications.        Early fracture signals the end of life of such a body. In        certain instances, for example when very dissimilar materials        are used for the PCD and the substrate, which can cause very        high residual tensile stresses, fracture may even result from        the manufacturing process alone. This is a contributor to a high        product reject rate even in standard production processes.    -   Conventional PCD cutters used in rock drilling applications        comprising a PCD element bonded to a hard metal substrate        element particularly suffer from early fracture problems caused        by crack propagation assisted by the macroscopic residual        stresses. Much of the prior art for such cutters involves        disclosures and inventions aimed at limiting such problems.        Aspects such as non-planar interfaces between the PCD layer and        carbide substrate, break-in chamfers at the PCD cutter leading        edge, partial removal of the metal in the PCD by leaching at the        surface, vacuum heat treatment annealing and, more recently,        functional grading of the PCD layer and the carbide substrate        have been developed and exploited to reduce the magnitude of the        tensile component and/or displace these tensile maxima to        positions remote from the free surfaces, and in so doing        favorably alter the crack behavior of cutters. These prior art        approaches have had some effect but do not provide a        comprehensive solution to early fracture problems of this nature        because the tensile components in the macroscopic residual        stress distributions cannot be eliminated.-   2. In principle, with the conventional approach, one could form a    PCD layer on any size and shape of the substrate. The thickness of    such a PCD layer in the direction of the infiltration is limited in    practice by any one or combination of three possibilities. Firstly,    above a thickness of about 3 mm the tensile component of the    residual stress can become very significant and can be dominant in    regard to failure of the PCD in manufacture or mechanically based    applications. Secondly, a practical limitation in the range of    molten metal infiltration results in insufficient metal for good    diamond sintering to occur beyond a certain thickness of PCD, after    which the desired properties of the material are lost. The    infiltration range depends upon the diamond particle size    distribution which determines the pore size distribution. A limited    range in thickness to a few millimeters before inadequate metal for    good diamond sintering is particularly the case for PCD wholly made    from or with a fine grain component of less than 10 micron    particles. Thirdly, directional infiltration of molten metal sweeps    impurities such as oxygen and its compounds with the melt front.    These impurities concentrate sufficiently at a particular range of    thickness where they can interfere with the diamond sintering    mechanisms leading to very poor quality PCD which now will have    inferior properties.    -   The second and third factors contribute to inhomogeneity in both        structure and composition of the PCD material. A consequence of        limiting the thickness of the PCD material construction to a        small number of millimeters is that large equi-axed three        dimensional shapes for the PCD material component greater than        this small dimension cannot be made. Thus, the PCD material        component of a three dimensional construction is limited to a        thin layer on the three dimensional substrate shape, no matter        its size or shape. This thickness limitation is only minimally        increased in the prior art by such means as metal powder        additions to the starting diamond powder source layer. This        inherently, of its very nature, limits the PCD material to high        metal contents and thus can progressively compromise the        structure and properties, and the homogeneity of such        structures.-   3. Structural and compositional in-homogeneities as a result of    directional molten metal infiltration, occur discontinuously    extending from the substrate which acts as the source of the molten    metal diamond sintering aid into the PCD layer. In the most common    case in which commercially available standard tungsten carbide    cobalt hard metals are used as the substrate, immediately above the    substrate a layer of up to a few tens of micro meters thick always    occurs where nearly all of the diamond has been taken into solution    by the molten cobalt allowing it to become saturated in dissolved    carbon. This layer will then have low diamond content with little or    no intergrowth between the remaining diamond grains. Above this    layer, the molten cobalt saturated in dissolved carbon can now    facilitate dissolution and re-precipitation of some of the diamond,    which provides the diamond to diamond bonding. Where tungsten    carbide cobalt hard metal substrates are used, the infiltrating    molten cobalt often carries with it tungsten in solution. The    tungsten, when it experiences the carbon now rapidly coming into    solution, reacts with this carbon and solid tungsten carbide    crystals precipitate. The tungsten carbide precipitation being    governed by the normal rules of nucleation and growth of a solid    phase in a liquid medium, results in tungsten carbide precipitates    being distributed inhomogeneously in the metallic network of the    PCD. Often, the tungsten carbide based inhomogeneity can be extreme    with regions in the PCD volume containing areas of many tens of    micro meters across, which are depleted in diamond and have a    dominant population of tungsten carbide precipitates. Such    inhomogeneity severely compromises the properties of PCD material    where they occur, resulting in inferior performance in application.    -   Local inhomogeneity in diamond/metal content also arises due to        the directional infiltration being unequal and/or not        simultaneous across the expanse of the boundary area between the        PCD and the substrate. This results in uncontrolled        structural/compositional variations spatially, which cause local        variations in PCD properties and, as such, can be considered as        unwanted defects.    -   The in-homogeneity described in this section gives rise to        residual stresses at the defined macroscopic scale of the PCD        body by virtue of the thermo elastic property differences        between the adjacent inhomogeneous parts of the material.-   4. Molten metal infiltration from a substrate to form PCD is limited    to the metal component of said substrate which is molten under    appropriate pressure and temperature conditions for diamond    recrystallisation to occur. The binder metallurgy of practical hard    metal materials is significantly limited and highly dominated by    cobalt. This is particularly the case for tungsten carbide based    hard metal materials which are generally the most highly developed    and superior materials for most applications. More rarely available    is titanium carbide hard metal which, however, is made mainly with    nickel as the binding metal. Using tungsten carbide/cobalt hard    metal material types for PCD substrates, which is overwhelmingly the    normal commercial situation, thus largely restricts such    conventional PCD products to cobalt based metallurgy for the    metallic network in the PCD material layer. The infiltrating cobalt    from such a substrate can only be alloyed with other metals to a    limited extent by adding metal powders to the diamond powder layer    during manufacture.    -   Alternatively, the prior art teaches the use of placing thin        metal layers between the substrate and the diamond powder layer.        This approach is also limited to available metals alloys in        strip form which of course will have to be alloyed further in        situ by the molten metal infiltrating from the substrate.    -   The present applicants have appreciated that both of the above        approaches to metallurgical modification for the PCD material        usually result in alloy inaccuracy and in-homogeneity in the PCD        layer due to the directional infiltration of the substrate        origin metal. Thus, whilst the applicants believe that in        principle any combination of transition metal elements which can        enable diamond crystallization may be used to form the diamond        intergrowth essential for PCD materials and the resultant metal        interpenetrating network, to date only a narrow set of        possibilities have been conventionally exploited and these are        mostly limited to cobalt as the main metallic component.

It is known that highly specific transition metal alloys with accuratecompositions can exhibit special and remarkable properties, such asmagnetic and thermal expansion properties. With conventional PCD made byinfiltration of the metal component in total or in part from a substrateit is impractical and often impossible to specify sufficientlyaccurately or arrive at chosen alloys in the PCD material to exploitspecial and desired properties of such specific alloys.

-   5. Micro residual stress at the scale of the diamond grain size and    associated metal between the grains arises during the drop to room    pressure and temperature during the manufacturing process. This is    due to the thermo-elastic mismatch between the diamond network and    particular metal interpenetrating network present. Typically, the    thermal mismatch derived residual stress is the dominant effect. The    elastic modulus and thermal expansion coefficient of transition    metal alloys are highly dependent upon the accurate and specific    alloy composition. This is true particularly for the coefficient of    thermal expansion. For example in the iron/nickel system, for very    specific alloys such as invar, Fe, 36% Ni, a linear coefficient    minimum of 1.5 ppm ° K⁻¹ can be obtained which can be compared with    the pure metal values of 12 and 13 ppm ° K⁻¹ for iron and nickel,    respectively. Deviations of 0.1% by weight in this alloy can result    in a doubling of the linear coefficient of expansion, showing the    high sensitivity to the alloy composition. Pure cobalt has a linear    coefficient of expansion of 13 ppm ° K⁻¹ and some of its alloys with    iron and nickel also exhibit similar lowered thermal expansion    behavior. The micro residual stress therefore will vary    significantly from place to place in a PCD material where the alloy    is inhomogeneous and not accurately determined. Thus due to the    inhomogeneity and inaccuracy of metallurgy typical of the    conventional PCD approach where infiltration from a substrate is    employed, micro residual stress management at the scale of the    diamond micro structural grain size is limited and impractical.-   6. In conventional PCD, other than pressure and temperature    conditions, the only real degree of freedom one has to determine the    type of PCD material is to choose and specify the size distribution    of the starting source diamond powder. In particular, once the    diamond starting particle size is chosen, the metal content of the    PCD material layer is restricted to a limited range. The latter is    as a consequence of the bed or layer of diamond particles being    exposed to a large reservoir of molten metal, in the normally large    substrate. PCD materials with low metal contents cannot be easily    accessed. Generally, in conventional PCD, the metal content of the    PCD material increases inversely with the diamond particle size.    Increasing the pressure of manufacture can decrease the metal    content but only to a limited extent. Therefore, the resultant    composition of conventional PCD material has been restricted and    limited and the choice of metal content and diamond size    distribution cannot be independently pre-selected and made over a    wide range. The result is that the metal content for each chosen    diamond size distribution is limited to a range of about 3 or 4    volume percent around the mean value which is typically about 6    volume percent for the very coarse grades and about 13 volume    percent for very fine grades such as 1 micron.    -   This is illustrated by FIG. 4 which is a plot of cobalt content        of PCD materials related to average grain size of the starting        diamond particles for PCD sintered by the conventional route and        shows the limited range of metal content (the field between the        dashed parallel lines, region 1) typical of historical        conventional PCD made with tungsten carbide hard metal        substrates. FIG. 4 also shows that, after many years of        development, conventional PCD is still largely confined to        diamond/cobalt ratios in the band 15 between the dotted lines.        This figure also shows the trend of increasing metal content        with average finer grain sizes.    -   The present applicants have appreciated that one of the        important limitations for conventional PCD is the inability to        achieve very high diamond contents, i.e., low metal contents,        particularly with fine diamond size distribution. A well        established example of this is 1 micron PCD which has not been        made conventionally with more than 86 to 88 volume percent        diamond content, i.e., less than 12 to 14 volume percent metal        content. It has been empirically determined in the art that        increases in pressure and temperature conditions of conventional        PCD manufacture are capable of lowering the metal content by        about 1 to 2 volume percent. The lower limit of metal content        which can readily be obtained for conventionally made PCD        materials with typical historically exploited diamond particle        size distributions is indicated for such historical conventional        PCD materials by the lower dashed line A-B in FIG. 4. This line        corresponds to the formula y=−0.25x+10, where y is the metal        content of the PCD in volume percent, and x is the average grain        size of the PCD material in micro meters. The field of metal        content below this line is not conventionally accessible using        the typical pressures and temperatures available with the use of        the presently developed commercial high pressure high        temperature equipment. As explained in numbered section 4 above,        the metal or alloy composition is also conventionally limited        and difficult to accurately and controllably vary. Generally,        therefore, in the conventional approach, the manufacturing        degrees of freedom such as grain size distribution, metal        content and metal alloy are co-dependent and not readily        independently pre-selected, chosen and varied.

The limitations and problems with respect to homogeneity, macroscopicand microscopic residual stresses, size and shape of the PCD body, andrestricted choice of material composition described above for the priorart conventional PCD bodies or constructions gives rise to poor orinadequate performance in many applications.

The present applicants have appreciated that the development of freestanding PCD bodies of any 3-dimensional shape, specifically engineeredto have high material homogeneity and with an absence of macroscopicresidual stress, and with an independently pre-selected greatly expandedchoice of PCD material structure and composition, with attendant microresidual stress control, is highly desirable. Some embodiments describedhereunder are directed at removing or ameliorating the limitations ofthe conventional approach to PCD bodies or constructions in which thepossibility of better exploiting the true potential of PCD materialsbecomes viable.

The removal or amelioration of the limitations of conventional PCDmaterials makes the applications indicated above more viable with thepotential of new applications becoming possible for PCD materials.

A free standing, single volume of PCD material is disclosed which ishomogeneous and free of residual stress at a macroscopic scale greaterthan ten times the average grain size, where the coarsest component ofgrain size is no greater than three times the average grain size.

The free standing nature of this PCD volume or body arises due to theabsence of a bonded substrate of a dissimilar material to the PCD. Theabsence of a substrate also means that the molten metal required forenabling the partial recrystallisation of the diamond particles to formthe particle to particle diamond bonding does not arise from long rangedirectional infiltration from such a substrate body. Rather, therequired molten metal is provided solely by an initial homogeneous,intimate and accurate combination or mass of diamond particles andsmaller, pure metal particles, grains or entities. The details of themethods employed to form such a mass of diamond and metal particles,which is homogeneous above a scale related to the average and maximumdiamond particle sizes, together with the means by which the homogeneityis progressively maintained during consolidation of the mass to form aso called green body of pre-selected size and shape and subsequentsintering of the diamond particles at high pressure and temperature, aredescribed below.

When the metal particles are exposed to appropriate high pressure andtemperature conditions such that the metal melts, the molten metal onlypermeates the surrounding interstices in the local vicinity of eachdiamond particle. On exposure of a mass of such diamond particle/metalcombinations to these conditions, this very short range permeation ofthe molten metal into the surroundings of each diamond engenders highhomogeneity of diamond and metal. This is illustrated in FIG. 3 which isa schematic diagram of the very localised or short range movement ofmetal during the sintering of diamond particles in the PCD. It shows thediamond particles 13 with well and homogeneously distributed, smallermetal particles 12. The metal movement is depicted by arrows 14 movingin all directions but only as far as neighbouring diamond particles. Thehigh purity of the diamond metal combination also ensured by embodimentsof the methods described herein helps the generation of high homogeneityso that third phase precipitates, such as oxides and tungsten carbideand the like, may be avoided.

The free standing volume or body of homogeneous PCD material is notbonded in any way to other material bodies during manufacture, be theyof a dissimilar material or of a different composition and structure ofPCD. Macroscopic residual stresses cannot therefore be generated duringreturn to room pressure and temperature at the end of the manufacturingprocess. Such a free standing PCD body may thus be considered to bemacroscopically stress free at a scale above which it is homogeneous,spatially invariant and considered to be made of one average propertymaterial. In the context of typical PCD materials, this scale may beconsidered to be greater than ten times the average grain size, wherethe coarsest component of grain size is no greater than three times theaverage grain size. Where the average diamond grain size is about 10 to12 micro meters and the maximum grain size is smaller than about 40micro meters this scale may be considered to be above 120 micro meters.Where the average diamond grain size is about 1 micro meter where themaximum grain size is about 3 micro meters, this scale may be consideredto be above 10 micro meters.

The long range directional infiltration of molten metal from a substratein conventional PCD manufacture as previously described, contributes tothe dimensions of the PCD in the direction of the infiltration beinglimited to about 3 mm. Some embodiments ensure or assist in themaintenance of diamond and metal homogeneity at each stage ofmanufacture of a free standing PCD body and employ short rangepermeation of molten metal during the sintering stage and therebyeliminate or substantially ameliorate the above-mentioned limitation.Consequently, the dimensions possible for the free standing, stress freePCD body in any orthogonal direction is not limited in such a way.Therefore, it is believed that any desired 3-dimensional shape may begenerated, which is not possible in the conventional PCD prior art.Moreover, embodiments of the methods described herein may provide nearnet size and shape capabilities so that accurate non distorted freestanding PCD bodies may be made.

The generation of PCD having valuable general shapes where one directionin the PCD body is significantly greater than any of the dimensions atright angles to it is believed to be possible. For example, columnarstructures where the cross-sectional area perpendicular to the axis iscircular (cylindrical shaped), elliptical or any regular or irregularpolyhedral shape can be made.

Alternatively, general shapes where one direction in the solid issignificantly less than any dimension at right angles to it may also bereadily made, for example, these shapes include discs and plates. Thelarge faces of the plates may be any regular or irregular polyhedron.

The near net shape capability of some of the embodiments of the methodsdescribed herein may allow 3-dimensional solids having high degrees ofsymmetry to be made, such as spheres, ellipsoids (oblate and prolate)and regular solids. The regular solids may include the five so-called“Platonic” solids, namely the tetrahedron, cube, octahedron, icosahedronand dodecahedron. The thirteen semi-regular, so called “Archimedes”solids which include the cuboctahedron, truncated cube, truncatedoctahedron, truncated dodecahedron and truncated tetrahedron may also bemade. Moreover, the generation of other convex polyhedra such as prisms,pyramids and the like are believed to be possible. In addition, PCDbodies formed as conical and toroidal shapes may be made, together withpolyhedral toroidal shapes. More generally, any irregular shape wherethe solid is bounded by one or more non-straight edge and one or morenon-flat surface may be possible. All of the 3-dimensional solid shapesdescribed above, be they of high symmetry or irregular may be modifiedby forming concave re-entrant surfaces. Such re-entrant surfaces may bebounded by flat polygonal faces, curved surfaces, irregular surfaces orany combination of these. Re-entrant surfaces may have particular valuewhere the free standing body is required to be mechanically attached toa foundation or another body. For example, a circumferential groove mayfacilitate the use of a split ring for interlocking purposes.

Practical dimensions for such 3-dimensional shaped free standing PCDbodies will however be limited by the dimensions and designcharacteristics of the high pressure high temperature apparatus used tomanufacture them. Large high pressure high temperature systems with asample volume of greater than 1.0 litre and with high pressure reactionvolumes of dimensions as large as 132 mm in diameter, have beendisclosed in the technical literature (Ref. 5). More recently, it hasbeen established in the art that high pressure systems with reactionvolumes of 2.0 litres or more are viable. Such systems may be eithermulti-axial (such as cubic) systems or belt type system, both of whichare known in the art. The latter belt type systems are favoured and arepractically more amenable to large reaction volumes because of theirability to maintain pressure by accommodating large volume changesduring the reaction processes.

Free standing PCD bodies made with in accordance with some embodimentsof the method described herein may be made such that the largestdimension in any direction in the body may fall within the range 5 to150 mm. For example, a free standing PCD body consisting of a rightcircular cylinder of 100 mm diameter and 100 mm long will have thelargest dimension along a body diagonal of 141.4 mm. Another example isa free standing PCD cube of edge length 85 mm, which has a face diagonalof 120.2 mm and a body diagonal of 147.2 mm. Another example of a smallfree standing PCD right circular cylinder which has its largestdimension within the quoted range, has a diameter of 4 mm and a lengthof 4 mm and a body diagonal of 5.66 mm.

Another serious practical difficulty appreciated by the presentapplicants leading to limitations in the conventional PCD prior art isthe limited metallurgical scope derived from infiltration from asubstrate. This is true even when metal powders are added to the PCDstarting diamond. The inherent metallurgical inhomogeneitycharacteristic of the conventional PCD approach which is a result ofdirectional infiltration of the required molten metal in turn results inan inability to permit creation and choosing of accurate and specificalloy compositions which are the same from place to place across thevolume of the PCD material. Indeed it is also very difficult for eventhe diamond to metal ratio to be invariant across the dimensions of thePCD volume or layer. It is well known that the properties of alloys areusually highly dependent upon very specific and accurately madecompositions. Moreover, PCD materials themselves exhibit properties verydependent upon accurate compositions. The general consequence thereforeof this for conventional PCD is that the true scope of composition andtherefore properties cannot be uniformly achieved across the dimensionsof the conventional PCD volume or layer.

In contrast, some embodiments of the methods described herein areunfettered by such inhomogeneity and inaccuracy problems of compositionas very accurate and specific wide ranging alloy compositions may bechosen and made invariant across the dimensions of the free standing PCDvolume.

The accuracy in diamond-to-metal ratio characteristic of someembodiments of the methods described herein results from the metal oralloy being smaller than the diamond particle sizes, and beinghomogeneously distributed and associated with each diamond particle.This is particularly true for the method where the metal(s) or alloy(s)of choice are decorated onto or associated with the surface of eachindividual diamond particle of the starting diamond powder. During thehigh pressure high temperature phase of the manufacturing process wherethe metal on each of the diamond particle surfaces is melted, the moltenmetal permeates the interstices between the diamond particles to a verylimited range between the surrounding particles. This ensures that thechosen diamond to metal ratio is constant and invariant across thedimensions of the free standing PCD body and homogeneous at amacroscopic scale. The scale above which this homogeneity and invarianceof composition occurs is dependent upon the grain size distribution ofthe PCD material and is smaller for smaller average grain sizes. Forexample where the average grain size is 1 micro meter and the maximumgrain size is about 3 micro meters the material can be considered to behomogeneous and spatially invariant above about 10 micro meters. Moregenerally, the macroscopic scale above which the PCD material isconsidered to be spatially invariant may be defined as at a scalegreater than 10 times the average grain size, where the largest grainsare no more than 3 times the average grain size.

The accuracy of the alloy composition in some embodiments describedherein may be achievable as a consequence of the use of molecularprecursors for the chosen metals in the methods described herein. Someof the molecular precursors such as nitrate or carbonate salts of themetals may be made as mixed crystals or solid solutions. This ispossible in the cases where the metal salts are isomorphous, i.e.,having the same crystallographic structure. In particular, this is truefor the carbonates of some transition metals such as iron, nickel,cobalt and manganese. Where the mixed molecular precursor is chemicallygenerated or precipitated by reacting a solution of soluble salts orcompounds, the accuracy of the specifically chosen metallic elementratio may be determined by easily provided concentration ratios of thesolutions of the source compounds of the chosen metals. One of theexamples of this is to create a combined mixed solution of metalnitrates in water and then to precipitate a mixed carbonate precursorfor the chosen alloy by reaction with sodium or ammonium carbonatesolutions. The use of mixed molecular precursors in this way enables thechosen metal elements to be combined at an atomic scale. In contrast,the conventional approach to PCD manufacture necessarily involvesalloying by virtue of melts, flowing and diffusing together which alwaysresults in spatial variation and inaccuracy.

Precursor compounds which may be dissociated and/or reduced to metalsand alloys are readily available for nearly all the metals of theperiodic table. Those precursors which can be reduced to metals or metalcarbides by reaction with carbon may be preferred. In particular, themetals of Group VIIIA of the periodic table can be exploitedindividually or in fully alloyed combinations. The metals chosen whollyor in part must however be capable of facilitating diamondcrystallization in order to create the necessary diamond particle toparticle bonding for PCD. An important implication of this is that theresultant metallic network of the PCD material has carbon in solidsolution usually to a maximum level as expressed in appropriatemetallurgical phase diagrams. In addition, metallic elements whichreadily form stable carbides will also be present in the metallicnetwork as carbide components. Thus, the metal alloys exploitable in PCDare the high carbon versions of such metals.

The free standing PCD bodies of some embodiments described herein due tothe high homogeneity and accuracy of composition may thus exploit thespecial properties of highly specific chosen compositions. For example,the metallic network may be chosen to be made from controlled expansionalloys which have highly specific elemental ratios. The thermo elasticproperties of the metallic network may therefore be chosen to bespecific from a wide range but, due to the homogeneity, be the same atall parts of the free standing PCD body. The range of linear coefficientof thermal expansion for the metallic network extends from magnitudestypical of elements such as cobalt (13 ppm ° K⁻¹ at room temperature) tothat typical of low expansion alloys like the high carbon version ofInvar (Fe, 33% Ni, 0.6% C, about 3.3 ppm ° K⁻¹ at room temperature, ref4). By accurate choice of the metallurgy of the metallic network thedifference in thermo elastic properties between the diamond network andthe inter-penetrating metallic network may be accurately chosen anddetermined. Together with the metal content which may be independentlychosen, such differences in the thermo elastic properties of the twointer-penetrating networks generate residual stresses at the scale ofthe microstructure during the quench to room conditions at the end ofthe manufacturing process. If the dominant stress generating effect isdue to the thermal shrinkage difference and the diamond expansioncoefficient, which is about 1 ppm ° K⁻¹ at room temperature, the diamondnetwork will be generally compressively stressed and the metallicnetwork generally under tension. The magnitude of this micro residualstress may be considered to be high when the linear coefficient ofexpansion of the metallic network is 10 to 14 ppm ° K⁻¹, medium for alinear coefficient of expansion of 5 to 10 ppm ° K⁻¹ and low for lessthan 5 ppm ° K⁻¹. Where the PCD body is homogeneous at a macroscopicscale as previously defined, these micro residual stresses sum to zero,resulting in the macroscopic residual stress being considered to be zeroand the free standing PCD body itself to be macroscopically stress free.When alloys with a coefficient of linear thermal expansion of less than5 ppm ° K⁻¹ are used the differences in elastic modulus between thealloys and diamond become more significant and the micro residual stressin the metallic network may in fact become compressive. Low expansionalloys such as iron, 33 weight % nickel, 0.6 weight % carbon which has aliterature value of elastic modulus and coefficient of linear thermalexpansion of 150 GPa and 3.3 ppm ° K⁻¹, respectively, are examples ofsuch alloys.

PCD bodies where the micro residual stress in the metallic network hasan overall compressive nature form some embodiments and are nowdisclosed.

The understanding of the present applicants is that micro residualstresses play a significant role in crack initiation and local crackcoalescence during mechanical applications of PCD materials. This may beconsidered as a key aspect of wear behaviour at the particle to particlelevel. Materials with a low propensity of micro cracking may hence bedeveloped using the approach and methods described herein.

The ability to independently choose and pre-select the metal content andmetallurgical type of the PCD material for the purpose of microstructural stress management as discussed above is an example of animportant and distinct character of some embodiments, namely, theability to independently choose and control the structural andcompositional variables.

Unlike in the conventional infiltration from a substrate PCD approachwhere initial choice of diamond particle size and size distributionlargely fixes or radically limits other variables, the method of someembodiments described herein allows independent choices and control ofthese variables and also the homogeneity of the end products to bespecifically engineered to be high. For example the metal content, metaltype, diamond size and size distribution may be independently chosen andcontrolled. As can be seen in FIG. 4, conventionally when fine grain PCDof about 1 micron average grain size is made by infiltration of metalfrom a hard metal substrate, the metal content is restricted to about 12to 14 volume percent.

In contrast, some embodiments described herein provide for the metalcontent to be chosen independently to the metal type and be anywhere inthe range from about 1 to 20 percent. Similarly, where a multimodalgrain size is chosen for the embodiments of a PCD body described hereinand the average grain size is about ten micro meters with the maximumgrain size about 30 micro meters, again the metal content may be chosenanywhere in the range from about 1 to about 20 percent. The metalcontent for conventional PCD material being restricted to around andclose to 9 volume percent, as illustrated in FIG. 4, no longer applies.The field of metal contents below the lower dashed line A-B in FIG. 4which correspond approximately to the formula y=−0.25x+10 where y is themetal content in volume percent and x is the average grain size of thePCD material in micro meters, may therefore be exploited using themethods described herein and embodiments of free standing PCD bodieswith metal contents in this field are envisaged.

The metallic network may be chosen to be most combinations andpermutations of the metals of the periodic table provided that diamondcrystallization can be facilitated by such metals, which also means thatthe alloys all have a high carbon content. This choice is madecompletely independently of average grain size, grain size distributionand diamond to metal ratio. Clearly, a greatly extended range of PCDmaterial types with their attendant properties can now be accessed. Yetanother feature of some embodiments described herein is that the elementtungsten will be absent unless deliberately included. This is incontrast to the dominant custom and practice of the conventional priorart PCD approach where tungsten carbide/cobalt hard metal substrates areused which inevitably result in tungsten being inhomogeneouslyincorporated as tungsten carbide precipitates in the PCD layer. Someembodiments of the methods described herein assist in allowing theincorporation of tungsten carbide as an added phase at controllable andhomogeneous levels if such compositions are chosen. Typically, PCDcompositions free of tungsten may, however, readily be made.

The metals and alloys which are capable of facilitating diamondcrystallization after melt, include any of and any combined permutationsor alloys of the transition metals of the periodic table whereby atleast one metal does not form stable carbide compounds at conditions oftemperature and pressure appropriate for diamond crystallization.Typical of these latter metals and preferred for diamond crystallizationprocesses are the Group VIIIA metals of the periodic table such as iron,nickel, cobalt and also the Group VIIA metal manganese. Transitionmetals which form stable carbides under typical diamondre-crystallization from metal solutions conditions include tungsten,titanium, tantalum, molybdenum, zirconium, vanadium, chromium andniobium. Some embodiments described herein allow the metallic network inthe PCD body to be accurately chosen combinations of iron, nickel,cobalt or manganese with the carbides of these elements. Notably,cobalt, tungsten carbide (WC) combinations ranging from high cobaltcontent to low cobalt content may be provided by some embodiments ofthese methods.

A further feature some embodiments occurs as a result of the absence ofmacroscopic residual stress, in that manufacturing pressure andtemperature conditions may be widely chosen as undesirable residualstress distributions from such pressure and temperature choices does notoccur. The conventional PCD approach suffers from significant increasesin residual stress distributions as higher pressures and temperaturesare used causing a high incidence of cracking and fracture of the PCDparts during manufacture. Thus, the approach of some embodimentsdescribed herein may allow the ready beneficial use of higher pressuresand temperatures. The benefits may include increased intergrowth ofdiamond particles and associated property improvements such as increasesin hardness, strength and thermal properties with increased diamond tometal ratio. When striving for PCD materials confined to particularlylow metal contents such as 1 or 2 volume percent, the convenience ofusing increased pressures and temperatures may allow fully dense PCDmaterial to be achieved.

Some embodiments of methods for producing free standing PCD bodies aredescribed in detail below which covers means of creating particulatemasses of diamond and metals and alloys, followed by techniques toconsolidate these masses into green bodies of pre-determined shapes andsizes and finally subjecting the green bodies to high pressure hightemperature conditions in order to sinter the diamond particles.

Methods to produce the free standing, three dimensional PCD body orconstruction, of any shape and up to about 100 mm in any dimension,which is macroscopically homogeneous in structure and composition andstress free at a macroscopic scale are described. This macroscopic scaleis dependent upon the grain size distribution of the PCD material anddefined to be greater than ten times the average grain size, with themaximum grain size being about three times the average grain size. Formost typical so called coarse grain sized PCD materials this is greaterthan about 0.2 mm (200 micro meters). For very fine grained PCDmaterials close to an average of 1 micron, this scale is above about 10micro meters. In order to achieve this, means of combining diamondpowders of predetermined particle size distribution with metals or metalalloys at least one of which is capable of facilitating diamondcrystallization are required. Typically, but not exclusively, diamondpowders with an average particle size of less than 20 micro meters maybe used. After melting the metals in a consolidated mass of the combineddiamond particles and metals, at appropriate pressure and temperatureconditions, the molten metal only permeates the mass from each diamondparticle into the regions between immediately surrounding particles.This short range permeation or infiltration is thought to contribute toand ensure the homogeneity of the PCD body and in turn may provide forthe PCD body to be macroscopically stress free.

The approaches and means used to make the mass or combination of diamondpowder and appropriate metals and alloys for subsequent sintering of thediamond particles at high pressure and temperature, may providehomogeneity in diamond size distribution, diamond to metal distributionand metal composition. This homogeneity of the powder mass orcombination may then provide for the homogeneity of the final sinteredPCD material body. Further, this may be facilitated if, preferably, theform of the metals or metal alloys is of metal particles, grains orentities which are smaller than the size of the diamond particles foreach chosen size or size range of diamond particles required to producePCD with a chosen desired grain size distribution.

FIG. 5 is a generalized flow diagram showing alternative approaches andpreferences for combining diamond powders with appropriate metals toform a mass of particulate material which, after forming into3-dimensional semi-dense so-called “green” bodies, is subjected to hightemperature and pressure conditions to melt or partially melt the metaland partially re-crystallize the diamond to create the free standing PCDbodies.

Methods according to one or more embodiments of creating a starting massof combined diamond particles and smaller metal(s) or alloy(s) make useof precursor compounds, which may be dissociated or reduced to form thesufficiently pure metals and alloys by heat treatment in controlledenvironments. Examples of such environments include vacuum orappropriate gases which have reducing gases present such as hydrogen orcarbon monoxide and the like. These precursors include compounds such assalts, oxides and organometallic compounds of the transition metals orany chemical compound which can be dissociated and or reduced to yieldat least one of the required metals. For final alloy formation theseprecursors may be mixed. Alternatively, individual precursor compoundswhich contain the elemental combination of the desired alloys may beused, for example, mixed salts such as iron nickel cobalt nitrates,Fe_(x)Ni_(y)Co_(z)(NO₃)₂ where x+y+z=1, and the like. This will engenderhighest accuracy of final alloy atomic composition and homogeneity.

Ionic compounds such as salts which can be dissociated and/or reduced toform pure metals may be examples of candidates for precursors. Examplesof some such salts are nitrates, sulphates, carbonates, oxalates,acetates and hydroxides of the transition metals.

Of particular interest for some embodiments are the oxalates of cobaltand nickel, CoC₂O₄ and NiC₂O₄ which decompose to the metal in inertatmosphere, such as nitrogen, at very low temperatures and above such as310 and 360° C., respectively (Ref 1). Such oxalates may be used inhydrated form, e.g. crystals of CoC₂O₄.2H₂O and NiC₂O₄.2H₂O ordehydrated form.

Nitrate salts, in particular cobalt(II) nitrate hexahydrate crystals,Co(NO₃)₂.6H₂O, nickel nitrate hexahydrate crystals, Ni(II) (NO₃)₂.6H₂Oand ferrous iron(II) nitrate hexahydrate crystals, Fe(NO₃)₂.6H₂O,respectively, may, in some embodiments, be preferred as crystallizedprecursors for the specific metals. Such nitrate crystals are easilydehydrated and dissociated at low temperatures approaching 200° C. andreduced to the pure metals above temperatures as low as about 350° C. inhydrogen containing gaseous environments (Ref. 2 and 3).

Alloy compositions may be obtained by mixing the salts or by the use ofmixed metal single compounds such as mixed salts. For exampleco-crystallized nitrates of iron, cobalt and nickel to form mixedcrystals such as Fe_(x)Co_(y)Ni_(z)(NO₃)₂ where x+y+z=1. One advantageof using such mixed salts may be that, on dissociation and/or reductionto the metallic state, the metals will already be mixed at the atomicscale, engendering maximum homogeneity in regard to alloy composition.

Carbonates are also excellent precursors for metals such as iron,nickel, cobalt, copper and manganese. On thermal dissociation andreduction these salts form particularly finely sized metals, often downto a few tens of nanometers.

When metals such as cobalt, nickel, iron, manganese or copper, aredesired to be combined with metals which form stable carbides duringdecomposition/reduction and/or diamond sintering, such as tungsten,molybdenum, chromium, tantalum, niobium, vanadium, zirconium, titaniumand the like, a useful approach is to use ionic compounds where theformer metals form the cation and the latter carbide forming metals formpart of the anion, such as in tungstates, molybdates, chromates,tantalates, niobates, vanadates, zirconates and titanates, respectively.Some important examples of such compounds are cobalt tungstate, CoWO₄,nickel molybdate, NiMoO₄ and cobalt vanadate, Co₃(VO₄)₂, respectively.

Intermetallic compounds such as CoSn may also be made bydissociation/reduction of precursors such as cobalt stannate, CoSnO₃.

Examples of oxides which may be used include ferrous and ferric oxide(Fe₂O₃ and Fe₃O₄), nickel oxide (NiO), cobalt oxides (CoO and Co₃O₄).The latter oxide, Co₃O₄, may be produced as micro meter sized aggregatesof 20 to 100 nm particles by the decomposition of cobalt carbonate inair at low temperatures such as 300 to 400° C. For final alloyformation, these precursors may be mixed.

Other precursor compounds for the metal(s) or alloy(s) may becrystallized from solution in liquids where the diamond powder ispresent as a solid suspension, FIG. 5 column 1. Some precursor compoundsare soluble in solvent liquids such as water or alcohols and may becrystallized from such solutions by reduction of temperature and/orevaporation of the solvent or protocols known in the art ofcrystallization from solution, where suitable degrees of supersaturationand or seeding may be exploited.

Stable suspensions of desired diamond particle size distributionsanywhere in the range of 0.1 to greater than 30 micro meters may beobtained when in water or alcohol, particularly when the suspension isvigorously stirred. After appropriate settling and decantation followedby drying procedures, a combination of solid precursor(s) for the metaland diamond results. The crystallization of the precursor is organizedsuch that the particle or crystal size is smaller than that of thediamond powder. Subsequently, dissociation and/or reduction of theprecursor by heat treatment in vacuum or reductive gases generates amass of diamond and smaller sized metal particles, grains or entities.Approaches where diamond suspensions are used, particularly when theyare continuously stirred, may engender excellent homogeneous mixing withcrystallized precursors. The liquid suspension medium for the diamondand solvent for the precursor compounds may be water or alcohols such asethanol and the like or any appropriate and convenient liquid. Wherepure water is used, preferred precursors for the metals are salts and inparticular nitrates. This is because all metal nitrates have a highsolubility in water and may readily be thermally dissociated and/orreduced to the pure metal by low temperature heat treatment. Again, inparticular cobalt(II) nitrate hexahydrate crystals, Co(NO₃)₂.6H₂O,nickel nitrate hexahydrate crystals, Ni(II) (NO₃)₂.6H₂O and ferrousiron(II) nitrate hexahydrate crystals, Fe(NO₃)₂.6H₂O, respectively, maybe used, for example, as crystallized precursors for the specificmetals. Such nitrate crystals are easily dehydrated and dissociated atlow temperatures approaching 200° C. and reduced to the pure metalsabove temperatures as low as about 350° C. in hydrogen containinggaseous environments (Ref 2 & 3). In addition, many of the metalnitrates may be co-crystallized as mixed crystals whereby atomic scalemixing of extremely accurate alloys may be achieved on dissociation andreduction to the metallic state.

Another class of precursor compounds for this approach are the oxalates,M_(x)(C₂O₄)_(y), x and y being dependent upon the valency of the metalM, as the anion is (C₂O₄)²⁻. Examples of oxalate salts which may be usedinclude cobalt oxalate dehydrate crystals, Co(II)C₂O₄.2H₂O, nickeloxalate dehydrate crystals, Ni(II)C₂O₄.2H₂O and ferrous iron oxalatedehydrate crystals, Fe(II)C₂O₄.2H₂O. Ferric oxalate pentahydratecrystals, Fe(III)₂(C₂O₄)₃.5H₂O may also be crystallized and used in thisapproach. These compounds may be very easily decomposed and/or reducedto the pure metal at low temperatures (Ref 1).

Transition metal acetate crystals may also be used in this approach,such as cobalt acetate quadrahydrate, Co(II)(C₃H₃O₂)₂.4H₂O, nickelacetate quadrahydrate, Ni(II)(C₃H₃O₂)₂.4H₂O crystals and ferrous ironacetate quadrahydrate, Fe(II)(C₃H₃O₂)₂.4H₂O crystals.

Superior accuracy and homogeneity of diamond to metal composition ratio,metal alloy composition and purity may be possible using the abovedescribed method. Another approach to creating a mass or combination ofdiamond powder and metal(s), however, involves chemical reaction(s) toform and/or precipitate the precursor compound(s) for the metal inliquid in the presence of diamond powder in suspension, as shown in FIG.5 column 2. Here the precursor is significantly insoluble in the chosensuspension liquid. The reactants to form the precipitated precursor areintroduced into the diamond suspension by adding solutions of solublecompounds. One or more of these solutions is a source of the desiredmetal or metals.

FIG. 6 is a schematic diagram for this approach and illustrates asolution of a compound which is a source of metal atoms or ions, 16, issimultaneously added together with a solution of reactants, 17, to acontinuously stirred suspension of diamond powder, 18. The metal sourcecompound and reactant from solutions 16 and 17 react to form precipitatecrystals or compounds which nucleate and grow on the diamond particlesurfaces. These crystals or compounds then decorate the diamond surfacesand are precursor(s) for pre-selected metal particles. A representativediamond particle, 19, is illustrated with a precursor compound, 20,which decorates the particle surface. Notable examples of this approachmay have the feature of the nucleation and growth of the precursorcompound on the surface of the diamond particles. In this way theprecursor compound(s) for the metal are attached to the diamond surfacesand may be said to decorate said surfaces. Often the precursor isdiscretely distributed and does not form a continuous coating of thediamond particle surfaces. Some precursors may however form continuouscoats on the diamond surfaces but on dissociation and reduction to themetallic state, the metal particles are discrete and discontinuouslydistributed and decorate the diamond surfaces. Examples of the latterare amorphous oxides formed by reaction of metal alkoxides with water,elaborated upon below.

To enhance the behavior of nucleation and growth of the precursor(s) onthe surfaces of the diamond particles, the surface chemistry of thediamond particles may be deliberately chosen and produced to suit thenucleation of the precursor(s). When the precursor compound beingprecipitated has an oxy-anion such as CO₃ ²⁻ or OH⁻, or is formed bypolycondensation, hydrophilic diamond surface chemistries based uponoxygen species such as −OH, —C═O or —C—O—C— and the like areappropriate. Means of accentuating such diamond surface chemistries arewell known in the art and include high intensity ultrasound treatment ofthe diamond in water. FIG. 6 includes a schematic representation of adiamond particle with the surface decorated in a crystalline precursorcompound.

The precursor compound being a surface decorant or coating, means thatthe carbon at the diamond surface in contact with the precursor may actas an efficient reducing agent for the metal precursor compound onsubsequent heat treatment. This carbothermal reduction of the precursormay be used solely or in conjunction with other dissociative orreductive steps such as the use of hydrogen gas as reducing agent. Wherethe precursor materials are in intimate contact with the diamondsurfaces as is the case with this approach, the resultant metal willtake in carbon from the diamond surface and contain carbon in solidsolution. Stable carbides may also form at such conditions. The amountof carbon in solid solution in the metal decorant is highly dependentupon the temperature chosen for dissociation and reduction of theprecursor. A guide to the carbon content to be expected for particularmetals and alloys can be obtained by regard to the literature phasediagrams of the particular metal and alloy with carbon. By way ofexample to illustrate this, consider FIG. 7, which is the binary cobalt,carbon phase diagram. The line labeled AB is the solid solubility limitof carbon in solid face-centred-cubic cobalt. If the dissociation,reduction of a precursor for cobalt to obtain the metal is carried outat 700° C., the carbon content of the resulting cobalt metal will begiven by this line at 700° C., namely about 0.2 atomic percent carbon,similarly if the dissociation, reduction is carried out at 1050° C., thecarbon content of the cobalt will be about 0.8 atomic percent carbon. Onquench to room conditions these carbon contents may be metastablymaintained. Thus the carbon content of the resultant metal on thediamond surfaces may be chosen and predetermined.

Moreover, if the heat treatment conditions are maintained at the chosentemperatures for time periods of sufficient length, the carbon in solidsolution in the metal may diffuse through the metal decorating thesurface and progressively transport carbon from the diamond surface andcome out of solution at the metal surface, forming a deposit ofnon-diamond carbon. When this occurs, by choice of temperature and timeof the heat treatment, chosen and controlled predetermined amounts ofamorphous and or nano-crystalline non-diamond carbon may be generated onthe metal surfaces. This non-diamond carbon component of the startingdiamond metal particulate mass may contribute to the efficientcrystallization of diamond which bonds the diamond particle or grainstogether in the final PCD body.

Superior, especially well inter-grown diamond networks may be producedby control of such a non-diamond carbon component of the starting mass.Lower temperature conditions for short periods may also be chosen,guided by the appropriate metal, carbon phase diagram so that thenon-diamond carbon is low or absent.

FIG. 8 shows schematic representations of a diamond particle 21 andmetal particles decorating the surface 22 thereof. The metal particlesmay comprise grains or other entities without and with significantamounts of non-diamond carbon. The metal particles may have theirsurfaces covered in amorphous non-diamond carbon, 23, dependent on thechoice of dissociation, reduction temperature. Temperatures chosen nearA in FIG. 7 do not result in detectable non-diamond carbon. Temperatureschosen near B in FIG. 7, result in significant formation of non-diamondcarbon, which cover the metal particles.

A character of the metal decorant particles, grains or entities whichresult from this preferred approach is that they are much smaller thanthe diamond particles themselves and do not form a continuous metalcoating. The metal decorants are typically from about 10 to just over100 nm in size. This may allow very fine, so called sub-micron diamondparticle sizes, from 0.1 to 1 micro meter to be accurately andhomogeneously combined with chosen metals. This may provide a means ofmaking PCD bodies of extremely fine diamond grain size less than 1 micrometer.

A further benefit of this diamond suspension technique is that it may bereadily and conveniently scaled to that required by commercial PCDmanufacturing, where batch quantities of several kilograms may berequired. This may be done by appropriate choice of suspension vesselsizes in conjunction with, where necessary, heat treatment furnacedesigns capable of continuous operation.

The following are examples of some chemical protocols for some metalswhich may be exploited using this reaction based precursor compoundgeneration approach, where the precursor nucleates and grows on thediamond surface. These are examples only and are not intended to belimiting.

Cobalt is the historically dominant metal used in PCD material. A veryconvenient source solute for cobalt is crystalline pure cobalt nitratesalt, Co(NO₃)₂.6H₂O. This is due to cobalt nitrate's very highsolubility in both water and ethyl alcohol, which are possible solventsand suspension liquids for some embodiments of the method. Cobaltnitrate in solution reacts with sodium or ammonium carbonate solution,Na₂Co₃ or (NH₄)₂CO₃, respectively to precipitate cobalt carbonatecrystals, CoCO₃, as indicated in equation (1) below for the sodiumcarbonate case.

$\begin{matrix}{{{{Co}\left( {NO}_{3} \right)}_{2}{soln}} + {{Na}_{2}{CO}_{3}\left. {soln}\mspace{14mu} \underset{suspension}{\overset{H_{2}O\mspace{14mu} {diamond}}{}}\mspace{14mu} {CoCO}_{3}\downarrow{+ 2} \right.{NaNO}_{3}{soln}}} & (1)\end{matrix}$

More generally, the nitrate solutions of any of the transition metals ofthe periodic table may be reacted with sodium or ammonium carbonatesolution to precipitate and decorate the surfaces of diamond particlesin suspension with corresponding water insoluble metal carbonates. Thereaction with different transition metal nitrate solutions may becarried out sequentially or simultaneously. A mixture of solutions ofnitrates may also be employed to precipitate mixed carbonate crystals,such as Fe_(x)Ni_(y)C_(z)CO₃ where x+y+z=1.

FIGS. 9 a and 9 b are scanning electron microscope (SEM) images of a 2micro meter diamond particle which has been decorated in very fine,approximately 100 nm long, whisker like cobalt carbonate crystals.Whisker-like crystals of cobalt carbonate are shown as decorating thesurfaces of 2 micro meter sized diamond particles. Cobalt carbonate is aprecursor compound for cobalt metal.

In order to form cobalt metal as a particulate decoration on the diamondparticle surfaces, such cobalt carbonate decorated diamond particles maybe heated in, for example, a flowing gas mixture of 10% hydrogen inargon, at a constant temperature chosen in the range 500 up to 1320° C.,for time periods of from several tens of minutes to a few hours. If thetemperature is maintained below about 850° C. for a chosen short time,no non-diamond carbon can be detected.

FIGS. 10 a and 10 b are SEM images of 4 micro meter sized diamondparticles decorated in about 22 weight % (10 volume %) cobalt afterreduction in 10% hydrogen argon gas mixture at 850° C. The cobalt metaldecorating particles or grains vary from about 10 to 120 nm in size. Inthis embodiment, no non-diamond carbon could be detected with SEM ortransmission electron microscope (TEM) techniques.

FIG. 11 is a TEM micrograph of a diamond particle decorated in cobaltmetal particles, 26, together with a schematic diagram of the diamondsurface, 25. Each cobalt metal particle or grain, 26, is surrounded by anon-diamond carbon halo, 27 on a hydrogenated diamond surface, 25. Thenon-decorated portion of the diamond surfaces will be hydrogenterminated after such a heat treatment as The schematic diagram of FIG.11 shows nano cobalt particles or grains decorating the surface of adiamond particle after reduction of cobalt carbonate decorant at 1050°C. for two hours in flowing 10% hydrogen/argon gas mixture. The hydrogentermination of the diamond surface where the metal decorant is absent isa useful feature of the some embodiments of the method when hydrogenheat treatment is included.

Insoluble hydroxides may also be precipitated and decorated onto diamondparticle surfaces in suspension. For example nickel hydroxide, Ni(OH)₂,may be generated by the reaction of nickel nitrate solution with sodiumhydroxide solution in water as indicated in equation (2) below.

$\begin{matrix}{{{{Ni}\left( {NO}_{3} \right)}_{2}{soln}} + {2\left. {{NaOH}{soln}}\mspace{14mu} \underset{suspension}{\overset{H_{2}O\mspace{14mu} {diamond}}{}}\mspace{14mu} {{Ni}({OH})}_{2}\downarrow{+ 2} \right.{NaNO}_{3}{soln}}} & (2)\end{matrix}$

The precipitative approach may also be applied to precursors whichcombine metals such as iron, nickel, cobalt, manganese, copper and thelike as cations with the metals of the periodic table which may readilyform stable carbides such as tungsten, molybdenum, chromium, tantalum,niobium, vanadium, zirconium, titanium and the like, as oxy-anions.

These precursors may include tungstates, molybdates, chromates,tantalates, niobates, vanadates, zirconates and titanates. For example,cobalt tungstate Co(WO₄)₂ may be decorated onto diamond particlesurfaces by the reaction of cobalt nitrate solution with sodiumtungstate solution in water as indicated in equation (3).

$\begin{matrix}{{{{Co}\left( {NO}_{3} \right)}_{2}{soln}} + {{Na}_{2}{WO}_{4}\left. {soln}\mspace{14mu} \underset{suspension}{\overset{H_{2}O\mspace{14mu} {diamond}}{}}\mspace{14mu} {CoWO}_{4}\downarrow{+ 2} \right.{NaNO}_{3}{soln}}} & (3)\end{matrix}$

After reduction of the cobalt tungstate precursor, diamond decoratedcobalt and tungsten carbide results where the atomic ratio of cobalt andtungsten is 50%. This chemical protocol may be combined with cobaltcarbonate precipitation such that any cobalt to tungsten atomic ratio inthe range 50 to close to 100% may be generated.

An alternative chemical protocol to introduce tungsten is to use thereaction of ammonium paratungstate (NH₄)₁₀W₁₂O₄₁ solution with dilutemineral acids such nitric acid, HNO₃ to precipitate tungstic oxide, W0₃as surface decorant, which in turn is readily reduced in the presence ofdiamond to form tungsten carbide particles. Precipitation of carbonatesafter that of the tungstic oxide, such as cobalt carbonate usingequation (1), may be done to co-decorate the diamond surfaces.

Two SEM micrographs are given in FIG. 12 showing the surface of diamondparticles of about 2 micro meters in size, decorated in both cobalt, 28,and tungsten carbide, 29, particles after reduction of such aco-decoration in 10% hydrogen, argon flowing gas mixture at 1050° C. Theprecursor used for the cobalt was cobalt carbonate and the precursorused for the tungsten carbide was tungstic oxide. TEM microscopy alsodetected significant amounts of non-diamond, mainly amorphous carbonforming a covering on the cobalt particles after such furnaceconditions. Very similar chemical protocols may be used to createdecorants involving molybdenum carbides.

Where it is desired to generate decorants involving the carbides of theso called good carbide forming metallic elements such as, in particular,titanium, tantalum, niobium, vanadium, zirconium, chromium and the likea preferred chemical route is to react dry alcoholic solutions of themetal alkoxides with water, with the diamond powder suspended inalcohol. When this is done, amorphous, micro-porous coats of the metaloxide form on the diamond particles. On subsequent heat treatment theseoxide coats form discrete decorations of metal carbide on the diamondparticle surfaces. A general formula for the metal alkoxides isM(OR)_(n), where n is dependent upon the valency of the metal M and R isa alkane group, such as methyl, —CH₃, ethyl, —CH₂CH₃, isopropyl, —C₃H₇and the like. The metal alkoxides reaction with the water to yieldhydroxides, as is given in equations (4), which then undergopolycondensation reactions to form the amorphous oxide coats as inequation (5).

$\begin{matrix}{\mspace{79mu} {{{M({OR})}_{n}{{alc}.{soln}}} + {{nH}_{2}{O\mspace{14mu} \underset{Suspension}{\overset{C_{2}H_{5}{OH}\mspace{14mu} {diamond}}{}}\mspace{14mu} {M({OH})}_{n}}} + {n{ROH}}}} & (4) \\{{{\,_{n\text{-}1}({OH})}M\text{-}{OH}} + {{HO}\text{-}{{M({OH})}_{n\text{-}1}\mspace{14mu} \underset{suspension}{\overset{C_{2}H_{5}{OH}\mspace{14mu} {diamond}}{}}\mspace{14mu} {\,_{n\text{-}1}({HO})}}M\text{-}O\text{-}{M({OH})}_{n\text{-}1}} + {H_{2}O}} & (5)\end{matrix}$

An example reaction for amorphous tantalum oxide, Ta₂O₅ is given inequation (6) where tantalum ethoxide, Ta(OC₂H₅)₅ is reacted with waterin ethyl alcohol, C₂H₅OH.

$\begin{matrix}{{2{{Ta}\left( {{OC}_{2}H_{5}} \right)}_{5}{{alc}.{soln}}} + {5H_{2}{O\mspace{14mu} \underset{suspension}{\overset{C_{2}H_{5}{OH}\mspace{14mu} {diamomd}}{}}\mspace{14mu} {Ta}_{2}}\left. O_{5}\downarrow{+ 10} \right.C_{2}H_{5}{OH}}} & (6)\end{matrix}$

After forming such micro-porous oxide coats, precursors for metals suchas cobalt, nickel, iron, manganese and the like, such as carbonates orhydroxides, may be precipitated into and onto the oxide coats using thechemical reactions already indicated. Cermet or hard metal likecompositions of combined decorations of these metals with carbides maythen be formed by appropriate heat treatment in reducing environments.

FIG. 13 shows an SEM micrograph of a multimodal diamond powder made upof fine diamond particles (about 2 micro meters in diameter) and coarserparticles (from about 15 to 30 micro meters in diameter), which has beendecorated in 5.3 weight % tantalum carbide (TaC) particles together with3 weight % cobalt particles. The precursor for the TaC was amorphousTa₂O₅ deposited onto the diamond surfaces by reaction (6). Aftersettling, washing and drying procedures, the diamond powder was thenco-decorated with cobalt carbonate crystals using the reaction ofequation (1). Subsequently the combined precursors were reduced to formthe TaC, cobalt metal co-decoration of FIG. 13 by heat treatment inflowing 5% hydrogen, nitrogen gas at 1100° C. for 3 hours. It may beseen in FIG. 13 that both the TaC particles 31 which appear bright inappearance and the cobalt metal particles 30 which appear duller inappearance are very much smaller than the diamond particles andhomogeneously cover both the coarse and fine diamond particles.

Free standing PCD bodies may then be made from masses of diamondparticles such as these, with their decorations of metal, metal carbidecombinations. In such cases the resultant metal, metal carbide networkof the PCD material may have cermet or hard metal carbide likecompositions. Some embodiments of such compositions include WC/Co,TaC/Co and TiC/Ni.

Any of these chemical reactions to form the precursor compound decorantson the diamond particle surfaces may be done in sequence and applied tothe pre-selected diamond powder as a whole or to any part or componentof the diamond powder in appropriate suspension media.

The diamond powder components may be based upon mass fractions or uponsize, size distribution or any desired combination of these. The part orcomponent of the desired diamond size distribution is first suspended inthe liquid medium and the chosen chemical reaction protocol(s) todecorate that component with chosen precursor(s) carried out.Subsequently, the remaining diamond powder component or part is addedand suspended. The act of suspension and attendant vigorous stirringprovides an efficient means of homogeneously mixing the decorated andundecorated portions of the diamond powder. In this way chosenpre-selected components of the diamond powder may be decorated in chosenmetal with the other components remaining undecorated after subsequentdissociation/reduction of the precursor(s) to the metal(s).

Also, differing amounts of the same precursor may be decorated ontodifferent mass and/or size fractions of the diamond powders bysequential adding of the components to the suspension, reaction vessel.

Alternatively, different amounts of and/or types of precursor(s) may bedecorated on chosen diamond powder components in separated suspensionvessels. Again a final combination of the suspensions can provideefficient homogeneous mixing of these components.

In addition, any of the diamond powder fractions or components may bemade up of diamond particles differing in respect to diamond type.Diamond particles of differing type are distinguished here in regard tothe variation in structure and/or quantity of lattice defects known inthe art. In particular nitrogen related lattice defects are exemplary,which are known to affect the material properties of diamond. Aconvenient way to differentiate diamond type is to use natural diamondas opposed to standard synthetic diamond, natural diamond havingtypically aggregated nitrogen lattice defects as compared to standardsynthetic diamond which contains single atoms of nitrogen substitutingfor carbon atoms at levels typically of about 100 ppm.

These means of associating different amounts and/or different metalcompositions with different diamond fractions or components may providea highly accurate and versatile way of manipulating the diamondsintering mechanisms at the local scale of the diamond particles and inturn engendering manipulation of structure and composition at such ascale. For example, if certain fractions remain free of metal duringinitial application of load and heat in the high pressure apparatus,diamond particle, point to surface contact for the particles of suchfractions can be un-fettered by metal decoration leading to enhancedplastic deformation of such particles. This in turn may be possible tofacilitate local enhanced diamond to diamond bonding. Further it may bepossible to associate immovable “unmelted” particles with some diamondparticle fractions and not others. For example metal carbide particlessuch as tungsten carbide, titanium carbide, tantalum carbide and thelike may be decorated onto and associated only with a particular sizefraction of the diamond. A vast number of PCD free standing bodyembodiments with novel compositions, structures and properties may inthis way be generated using such prepared decorated diamond powder,metal combinations or masses.

The homogeneous mass of diamond and metal is consolidated to form aso-called “green body” of desired size and 3-dimensional shape. Means offorming a green body include simple die set compaction, isostaticcompaction, gel casting, injection moulding and the like and any othertechnique or procedure known in the art. Where isostatic compaction isused, hot isostatic procedures are preferred due to superior strength ofthe green bodies occurring. Preferences amongst such means to producegreen bodies may be determined by the degree to which each technique canmaintain general compositional and special homogeneity. Temporaryorganic binders such as methyl cellulose, polyvinyl alcohol, polyvinylbitherol and the like may be employed to aid with green body integrityand of sufficient strength for practical handling.

The homogeneous green body is then encapsulated such that it may becontained and isolated from the pressure and temperature media andstructures of high pressure and high temperature cells, capsules orreaction chambers as well known in the art of polycrystalline diamondmanufacture. Where the 3-dimensional shape of the desired PCD body isgeometrically simple canisters made from refractory metals may be used.Where general convex 3-dimensional shapes of the PCD body are desired,appropriate canisters may be moulded from refractory metals. Theencapsulation material or metal canisters are preferably organised sothat they may be evacuated and sealed again as had been established andis well known in the art. Removing atmospheric gases from the porositiesof the green body and sealing the green body's encapsulation materialsto maintain a vacuum in the porosities is a preference. Prior to thesealing of the encapsulation materials or canisters or temporary organicbinders which may have been employed in forming the green bodies must beremoved by procedures such as heat treatment and the like.

The green bodies in their sealed encapsulations are then assembled intoa cell or capsule comprising pressure and temperature transmitting mediaand heating element structures as known in the art. The design of thecell or capsule is chosen so that pressure and temperature gradientsexperienced by the green body at its sintering conditions are minimised.Low shear strength pressure transmitting materials such as ionic saltsoften combined with ceramic powders may be used, for example, sodiumchloride combined with zirconia, ZrO₂. These measures assist in enablingthe homogeneity of the structure and composition of the green body to betranslated into corresponding homogeneity of the PCD body on sintering.Moreover, in this regard, the pressure and temperature time cycle may bechosen so that simultaneous and or symmetrical melting of the metalcomponent in the green body occurs.

A further precaution to engender stress free and crack free standing PCDbodies may be to release the pressure during the end phase of themanufacturing cycle with the maintenance of sufficient temperature tomaintain the pressure transmitting media of the cell or capsule in asplastic a state as possible. The homogeneity of the green body togetherwith the precautions outlined above is necessary so that the shrinkageduring sintering of the diamond particles is equal in all orthogonaldirections. In this way, the pre-selected 3-dimensional shape of thegreen body may be maintained and translated to the final free standingPCD body. In addition, the degree and magnitude of the equi-directionalshrinkage for each variant or embodiment of PCD material and body may beempirically determined. Some of the embodiments of the methods describedherein thus may allow free standing, macro stress free PCD bodies of netor near net size and shape to be generated.

This feature of net or near net size and shape may provide practical andcommercial viability and attractiveness as further sizing and shaping isminimized or not required.

The green bodies generated by the above methods are subjected to highpressure, high temperature conditions for appropriate times to causesintering of the diamond particles and form the free standing PCDbodies. Each specific chosen metallic composition may require specifictemperature, pressure and time cycles to be determined empirically suchthat the re-crystallized diamond is of good quality crystal and islargely defect free. Typical pressure and temperature conditions are inthe range of 5 to 15 GPa and in the range of 1200 to 2500° C.respectively. Preferably pressures in the range 5.5 to 8.0 GPa alongwith temperatures in the range 1350 to 2200° C. are used.

Some embodiments are described in more detail below with reference tothe examples, which are not intended to be limiting.

EXAMPLES Example 1

PCD free standing, macro residual stress free, bodies each comprising anintergrown diamond network with a monomodal, mean grain size of close to1 micro meter with an inter-penetrating metallic network made up ofindependently pre-selected alloy made up of 95 weight % cobalt and 5weight % nickel were manufactured. The overall diamond content waspre-selected independently of the diamond size distribution and alloycomposition to be about 93 volume % with the metal being a corresponding7 volume %. The PCD body was a right cylinder 13 mm in diameter and 8 mmlong. The method as outlined in FIG. 5 column 2 was used whereby theprecursor for the metallic component of the PCD body was reactivelycreated in a water liquid suspension of starting diamond particles andwas caused to nucleate and grow on the surfaces of the starting diamondparticles. The following sequential steps and procedures were carriedout in order to so manufacture this PCD free standing body.

-   a) A mass of combined diamond particles and metallic materials was    created in the following manner.    -   100 g of monomodal diamond powder of mean particle size of about        1 micro meter, extending from about 0.75 to 1.25 micro meters,        was suspended in 2.5 litres of de-ionised water. The size        distribution had only one maximum at the average particle size        of 1 micro meter. This type of size distribution had been        designated as monomodal. The diamond powder had previously been        produced by crushing and classifying procedures known in the        art, the source material for which was conventional, commercial        synthetic type Ib diamond abrasive. The diamond powder had also        been previously heated in a mixture of sulphuric acid and nitric        acid which after washing in de-ionised water ensured that the        powder was now hydrophilic with a surface chemistry dominated by        oxygen molecular species such as —OH, —C—O—C—, —C═O and the        like. To the suspension a mixed aqueous solution of cobalt and        nickel nitrate and an aqueous solution of sodium carbonate were        slowly and simultaneously added while the suspension was        vigorously stirred. Equation (7) below was used to calculate the        required amounts of cobalt and nickel nitrates.

0.95Co(NO₃)₂+0.05Ni(NO₃)₂+Na₂CO₃=Co_(0.95)Ni_(0.05)CO₃+2NaNO₃  (7)

-   -   The mixed cobalt and nickel nitrate aqueous solution was made by        dissolving 89.25 g of cobalt nitrate hexahydrate, Co(NO₃)₂.6H₂O,        crystals and 4.71 g of nickel nitrate hexahydrate,        Ni(NO₃)₂.6H₂O, crystals in 200 ml of de-ionised water. In this        way the atomic ratio of cobalt:nickel was 95:5. The sodium        carbonate aqueous solution was made by dissolving 35 g of sodium        carbonate, Na₂CO₃, in 200 ml of de-ionised water. The mixed        cobalt, nickel nitrate and sodium carbonate reacted to form        mixed cobalt nickel carbonate precipitate crystals.

The mixed cobalt nickel carbonate precursor, nucleated and grew on thediamond particle surfaces and formed a discrete set of particlesdecorating the surfaces. The sodium nitrate product of the reaction,equation 7, being highly soluble in water was then removed by a fewrepeated cycles of decantation and washing in de-ionised water. After afinal wash in pure ethyl alcohol the precursor decorated diamond powderwas dried under vacuum at 60° C.

The dried powder was then placed in an alumina ceramic boat with a loosepowder depth of about 5 mm and heated in a flowing stream of argon gascontaining 5% hydrogen. The top temperature of the furnace was 1050° C.which was maintained for 2 hours before cooling to room temperature.This furnace treatment dissociated and reduced the mixed cobalt-nickelcarbonate to form alloy particles decorating the surfaces of the diamondparticles. In this way it was ensured that the alloy metal particleswere always smaller than the diamond particles with the alloy beinghomogeneously distributed.

FIG. 15 is an SEM micrograph showing the fine cobalt nickel carbonatecrystals decorating the 1 micron diamond particle surfaces. It may beseen that the precursor crystals or particles are all significantlysmaller than the diamond particles.

FIG. 16 is an SEM micrograph showing the alloy metal particlesdecorating the diamond particle surfaces. The alloy metal particlescomprise 95% cobalt, 5% nickel alloy metal particles which are shown asdecorating the surfaces of 1 micron diamond particles. The conditions ofthe heat treatment also caused amorphous non-diamond carbon to form atthe surfaces of the cobalt-nickel alloy particles. The resultant powdermass had a black appearance. The powder mass was stored under drynitrogen in an air-tight container.

-   b) 4.4 g fractions of the diamond-metal powder mass were then    pre-compacted into a niobium cylindrical canister using a uni-axial    hard metal compaction die. A second niobium cylindrical canister of    slightly larger diameter was then slid over the first canister in    order to surround and contain the pre-compacted powder mass. The    free air in the porosities of the pre-compacts was then evacuated    and the canisters sealed under vacuum using an electron beam welding    system known in the art. The canister assemblies were then subjected    to cold isostatic compaction at a pressure of 200 MPa to consolidate    to a high green density and to eliminate spatial density variations.    In this way homogeneous green bodies were produced with measured    densities of about 2.7 g·cm⁻³, which corresponds to a porosity of    approximately 35% by volume.-   c) Each encapsulated cylindrical green body was then placed in an    assembly of compactable ceramic, salt components suitable for high    pressure high temperature treatment as well established in the art.    The material immediately surrounding the encapsulated green body was    made from very low shear strength material such as sodium chloride.    This provides for the green bodies being subjected to pressures    which approach a hydrostatic condition. In this way pressure    gradient induced distortions of the green body may be mitigated.    -   The green bodies were subjected to a pressure of 7.5 GPa and a        temperature of approximately 1950° C. for 1 hour using a belt        type high pressure apparatus as well established in the art.        During the end phase of the high pressure high temperature        procedure the temperature was slowly reduced over several        minutes to approximately 750° C., maintained at this value and        then the pressure was reduced to ambient conditions. The high        pressure assembly was then allowed to cool to ambient conditions        before extraction from the high pressure apparatus. This        procedure during the end phase of the high pressure high        temperature treatment was thought to allow the surrounding salt        media to remain in a plastic state during the removal of        pressure and so prevent or inhibit shear forces bearing upon the        now sintered PCD body. The final dimensions of the free standing        PCD cylindrical body were then measured and the shrinkage        calculated.-   d) SEM image analysis was undertaken on sectioned and polished    samples of the PCD bodies. These showed a well sintered continuous    network of diamond and an interpenetrating network of metal. There    was an absence of other material phases such as oxides and carbides.    In order to assess the homogeneity of the microstructure, SEM image    fields of at least 10 times by 10 times the average grain size for    sections and polished samples taken in both axial and diametral    directions were considered and compared. For this specific example,    where the average grain size was close to 1 micro meter, ten micro    meters by ten micro meters image fields were compared from place to    place on the polished cross-sections. The magnification employed was    ×10,000. Across the axial section, 9 fields were chosen to be    representative of the centre and the edge positions. In addition,    across the diametral section a further 5 centre to edge positions    were compared. In terms of the image contrast and geometric pattern    of the diamond grains and metal pool, no difference could be seen.    No grains greater than 3 micro meters were found. It was therefore    concluded that the PCD material microstructure was invariant from    image to image showing that the material was homogeneous above this    scale, i.e., above the scale of 10 times the average grain size, in    this particular case above the 10 micro meter scale. As explained in    the previous sections, since this specific example was made from one    composition of PCD material, then it implies that the free standing    PCD body was macroscopically stress free above this scale.    -   To check this, a biaxial strain gauge was attached to one face        of a PCD cylinder and the cylinder cut in half midway along its        axis using electro discharge machining (EDM). It was noted that        no change of strain was observed. If the PCD free standing body        had a macroscopic residual stress distribution across its        dimension, then removing half of the body would inevitably have        resulted in a strain response. Since no strain response was        observed it was concluded and confirmed that the free standing        body was macroscopically stress free.    -   A finite element method was used in order to numerically assess        the micro residual stress magnitude for this composition of PCD        material. The elastic modulus assumed in the calculations for        diamond and the 95% Co-5% Ni alloy were 1050 and 200 GPa,        respectively. The difference in linear thermal expansion        coefficient was 11 ppm ° K⁻¹. The linear thermal expansion        coefficient for this alloy falls within the range 10 to 14 ppm °        K⁻¹. The micro residual stress for this particular PCD material        would therefore be considered by the previous definitions to be        in the “high” category. The calculated micro residual principal        tensile stress magnitude in the metallic network using the        Finite Element analysis with its attendant assumptions was 2300        MPa which was consistent with the micro residual stress being        considered as high.

Example 2

PCD free standing, macro residual stress free, bodies each comprising anintergrown multimodal diamond network where the grain size distributionextends from about 2 micro meters to about 30 micro meters with a meangrain size of close to 10 micro meter together with an inter-penetratingmetallic network made up of pure cobalt were manufactured. The overalldiamond content was pre-selected independently of the diamond sizedistribution and metal composition to be about 91 volume % with themetal being a corresponding 9 volume %. The PCD body was a rightcylinder 16 mm in diameter and 16 mm long. The method outlined in FIG. 5column 2 was used whereby the precursor for the metallic component ofthe PCD body was reactively created in a water liquid suspension ofstarting diamond particles and was caused to nucleate and grow on thesurfaces of the starting diamond particles. The following sequentialsteps and procedures were carried out in order to so manufacture thisPCD free standing body.

-   a) A mass of combined diamond particles and metallic materials was    created in the following manner.

100 g of diamond powder was suspended in 2.5 litres of de-ionised water.The diamond powder comprised 5 separate so-called monomodal diamondfractions each differing in average particle size. The diamond powderwas thus considered to be multimodal. The 100 g of diamond powder wasmade up as follows: 5 g of average particle size 1.8 micro meters, 16 gof average particle size 3.5 micro meters, 7 g of average particle size5 micro meters, 44 g of average particle size 10 micro meters and 28 gof average particle size 20 micro meters. This multimodal particle sizedistribution extended from about 1 micro meter to about 30 micro meters.

The diamond powder had been rendered hydrophilic by prior acid cleaningand washing in de-ionised water. To the suspension an aqueous solutionof cobalt nitrate and a separate aqueous solution of sodium carbonatewere simultaneously slowly added while the suspension was vigorouslystirred. The cobalt nitrate solution was made by dissolving 123.5 gramsof cobalt nitrate hexahydrate crystals, Co(NO₃)₂.6H₂O, in 200 ml ofde-ionised water. The sodium carbonate solution is made by dissolving 45g of pure anhydrous sodium carbonate, Na₂CO₃ in 200 ml of de-ionisedwater. The cobalt nitrate and sodium carbonate reacted in solution asper equation (1), in the presence of the suspended diamond powder andcobalt carbonate crystals nucleated and grew on the diamond particlesurfaces. The cobalt carbonate precursor compound for cobalt, took theform of whisker shaped crystals decorating the diamond particle surfacesidentical in form to those shown in FIGS. 9 a and b. The sodium nitrateproduct of reaction was removed by a few cycles of decantation andwashing in de-ionised water. The powder was finally washed in pure ethylalcohol, removed from the alcohol by decantation and dried under vacuumat 60° C.

The dried powder was then placed in an alumina ceramic boat with a loosepowder depth of about 5 mm and heated in a flowing stream of argon gascontaining 5% hydrogen. The top temperature of the furnace was 700° C.which was maintained for 2 hours before cooling to room temperature.This furnace treatment dissociated and reduced the cobalt carbonateprecursor to form pure cobalt particles decorating the surfaces of thediamond particles. In this way it was ensured that the cobalt particleswere always smaller than the diamond particles with the cobalt beinghomogeneously distributed. The conditions of the heat treatment werechosen with reference to the cobalt carbon phase diagram of FIG. 7. At700° C. it may be seen that the solid solubility of carbon in cobalt islow. Thus the formation of amorphous non-diamond carbon at thistemperature is very low and no non-diamond carbon could be detected inthe final diamond-metal particulate mass. The resultant powder mass hada pale light grey appearance. The powder mass was stored under drynitrogen in an air-tight container.

-   b) 13.4 g fractions of the diamond-metal powder mass were then    pre-compacted into a niobium cylindrical canister using a uni-axial    hard metal compaction die. Right cylindrical green bodies with    homogeneous porosity distribution, encapsulated and vacuum sealed in    niobium canisters were then produced using the procedures specified    in Example 1. The diameter and length of each encapsulated green    body cylinder were measured and the diameter and length of each    cylindrical green body itself calculated using knowledge of the wall    thicknesses of the canisters. Both the average diameter and length    of the green body cylinders were calculated to be 18.25 mm.-   c) Each of the encapsulated green bodies was then subjected to high    pressure and high temperature conditions in order to cause diamond    particle to particle bonding via partial diamond recrystallisation.    The procedures specified in Example 1 were used except that the    pressure and temperature conditions were significantly lower,    specifically 5.6 GPa and 1400° C. Again, the temperature during the    return to room pressure at the end stage of the manufacturing cycle    was maintained close to about 750° C. This precaution was intended    to mitigate any possible shear stresses being applied during the end    stage of the cycle.-   d) SEM image analysis was undertaken on sectioned and polished    samples of the PCD bodies. These showed a well sintered continuous    network of diamond and an interpenetrating network of metal. There    was an absence of other material phases such oxides and carbides.    Hundred micro meters by hundred micro meters image fields were    compared from place to place on the polished cross-sections. It was    found that the PCD material microstructure was invariant from image    to image showing that the material was homogeneous above this scale.    This implies that the free standing PCD body is macroscopically    stress free above this scale.    -   A finite element method was used in order to numerically assess        the micro residual stress magnitude for this composition of PCD        material. The elastic modulus assumed in the calculations for        diamond and the Co metallic network was 1050 and 200 GPa,        respectively. The linear coefficient of thermal expansion for        cobalt is 13 ppm ° K⁻¹, which falls in the range of 10 to 14 ppm        ° K⁻¹. The calculated micro residual principal tensile stress        magnitude in the metallic network using the Finite Element        analysis with its attendant assumptions was in excess of 2000        MPa which was consistent with the micro residual stress being        considered as high.

The dimensions of each final cylindrical PCD free standing body weremeasured at various positions along the length of the cylinders and thesquareness was checked. It was evident that only minimal geometricdistortion had occurred indicating the achievement of near net shape.The average shrinkage of both diameter and length due to the sinteringof the material was 12%. Knowledge of this shrinkage factor for thisparticular PCD material allows the final dimension to be pre-selected,thus making near net sizing possible.

Example 3

PCD free standing, macro residual stress free, bodies each comprising anintergrown diamond network where the grain size distribution extendsfrom about 2 micro meters to about 30 micro meters, with a mean grainsize of close to 10 micro meter together with an inter-penetratingmetallic network made up of pure cobalt were manufactured. The overalldiamond content was pre-selected independently of the diamond sizedistribution and metal composition to be about 95 volume % with themetal being a corresponding 5 volume %. The preparation method in thisexample was changed compared to that of Example 2 with the intention ofcreating favourable micro structural consequences related to degree ofintergrowth and contiguity of the diamond grains. The basis of thechange of preparation method was that the precursor compound for themetal component of the PCD was decorated onto a pre-selected portion ofthe diamond powder. In this example, the pre-selected portion upon whichall of the metal was decorated was made up of the three coarsest sizefractions which also correspond to about half of the total diamondparticle surface area.

-   a) A mass of combined diamond particles and metallic materials was    created in the following manner.    -   Two portions of diamond powder were used totalling 100 g. One        portion of 79 g of diamond powder made up of 7 g of average        particle size 5 micro meters, 44 g of average particle size 10        micro meters and 28 g of average particle size 20 micro meters        was suspended in 2.5 litres of de-ionised water. This portion of        the diamond powder comprised 3 separate so-called monomodal        diamond fractions each differing in average particle size. The        diamond particle surface area of this portion of the diamond        powder corresponded to approximately 50% of the total surface        area of all the powder. The remaining portion of total mass 21 g        of diamond powder made up of 5 g of average particle size 1.8        micro meters and 16 g of average particle size 3.5 micro meters        was retained. To the suspension an aqueous solution of cobalt        nitrate and a separate aqueous solution of sodium carbonate were        simultaneously slowly added while the suspension was vigorously        stirred. The cobalt nitrate solution was made by dissolving 65.7        g of cobalt nitrate hexahydrate crystals, Co(NO₃)₂.6H₂O, in 200        ml of de-ionised water. The sodium carbonate solution was made        by dissolving 24 g of pure anhydrous sodium carbonate, Na₂CO₃ in        200 ml of de-ionised water. It was assumed that the cobalt        nitrate and sodium carbonate reacted in solution as per equation        (1). In the presence of the suspended diamond powder, cobalt        carbonate crystals nucleated and grew on the diamond particle        surfaces. While continuing the stirring of this suspension, the        remaining 21 g portion of diamond powder was added. Since the        reaction generating the cobalt carbonate precursor was complete        prior to this addition, this fine sized diamond powder portion        remained un-decorated. Incorporating this portion in suspension        served to homogeneously mix the two portions of diamond powder.        A dry particulate mass of powder was then made using the washing        and drying procedures of Example 2.-   b) Free standing PCD bodies were then made using this mass of    combined diamond and cobalt using the green body consolidation and    high pressure high temperature sintering procedures as described in    Example 2.-   c) SEM image analysis procedures were carried out on sectioned and    polished samples. It was concluded that excellent diamond grain    contiguity with good general homogeneity had resulted.

Example 4

PCD free standing, macro residual stress free, bodies were made with thesame diamond composition and size distribution as in Example 2. Themetal was pre-selected independently to be 9 volume percent pure Nickel.As in Example 2, the method as outlined in FIG. 5 column 2 was used. Thefollowing sequential steps and procedures were carried out in order toso manufacture this PCD free standing body, differing from Example 2 inthat the precursor compound was a hydroxide as opposed to a carbonate.

-   a) A 100 g of diamond powder identical to that used in Example 2 was    suspended in 2.5 litres of de-ionised water. While continuously    stirring the suspension, an aqueous solution of nickel nitrate was    slowly added. Simultaneously an aqueous solution of sodium hydroxide    was slowly added. The nickel nitrate solution was made by adding    96.8 g of nickel nitrate hexahydrate, Ni(NO₃)₂.6H₂O, to 200 ml of    de-ionised water. The sodium hydroxide solution was made by adding    27 g of pure sodium hydroxide crystals, NaOH, to 200 ml of    de-ionised water. Insoluble nickel hydroxide, Ni(OH)₂, was    precipitated as per equation (2), and decorated the surfaces of the    diamond particles. In this case nickel hydroxide was the precursor    compound for nickel metal. A dry mass of the diamond powder    decorated in the nickel hydroxide was then obtained by a few cycles    of settling, washing in pure water and drying under vacuum at 60° C.    The mass of diamond powder decorated in nickel hydroxide was then    heated in a vacuum furnace at a top temperature of 800° C. for 1    hour. The nickel hydroxide was converted into nickel metal which    decorated the diamond particle surfaces. The solid solubility of    carbon in nickel at 800° C. is low and very little non-diamond    amorphous carbon was formed. The resulting mass had a grey    appearance.-   b) Right cylindrical green bodies were then made using the same    procedures as given in Example 2.-   c) Each of the encapsulated green bodies was then subjected to high    pressure and high temperature conditions in order to cause diamond    particle to particle bonding via partial diamond recrystallisation.    The pressure, temperature, time cycle was identical to that of    Example 2.-   d) SEM image analysis was carried out and showed a well sintered    continuous network of diamond, with homogeneity of diamond and    nickel. There was an absence of other material phases such oxides    and carbides, in particular, indicating the presence of only pure    nickel metal. The SEM images showing fields of about 100×120 micro    meters taken from various parts of polished cross sections were    identical in regard to the distribution of diamond and metal. This    indicated that above this scale, the material was homogeneous and    could be considered to be macroscopically stress free.

Example 5

PCD free standing, macro residual stress free, bodies were made with thesame diamond composition and size distribution as in Examples 2 and 4.The metal was pre-selected independently to be 9 volume percent of airon, 33 weight percent nickel alloy. As in Examples 2 and 4, the methodas outlined in FIG. 5 column 2 was used. The following sequential stepsand procedures were carried out in order to so manufacture this PCD freestanding body. The precursor compound was a mixed ferrous, nickelcarbonate.

-   -   a) A 100 g of diamond powder identical to that used in Examples        2 and 4 was suspended in 2.5 litres of de-ionised water. While        continuously stirring the suspension, an aqueous mixed solution        of ferrous nitrate and nickel nitrate was slowly added.        Simultaneously an aqueous solution of sodium carbonate was        slowly added. The mixed ferrous nitrate, nickel nitrate solution        was made by adding 79.4 g of ferrous nitrate hexahydrate        crystals, Fe(NO₃)₂.6H₂O, and 37.6 g of nickel nitrate        hexahydrate, Ni(NO₃)₂.6H₂O, to 200 ml of de-ionised water. The        sodium carbonate solution was made by adding 44 g of pure        anhydrous sodium carbonate, Na₂CO₃, to 200 ml of de-ionised        water. A mixed ferrous iron, nickel carbonate, of nominal        formula Fe_(0.67)Ni_(0.33)CO₃ was precipitated and decorated the        diamond particle surfaces. A dry particulate mass of diamond        decorated in this alloy precursor was then produced by several        cycles of settling decantation and washing in pure water        followed by drying under vacuum at 60° C. The mass of diamond        powder decorated in the mixed carbonate was then heated in a        vacuum furnace at a top temperature of 850° C. for 1 hour. The        mixed carbonate was converted into an iron nickel alloy which        decorated the diamond particle surfaces. A small sample of        resulting particulate mass was taken and dissolved in nitric        acid in order that chemical analysis techniques such as        inductively coupled plasma spectroscopy (ICP) could be applied        to determine and confirm the alloy composition. The alloy was        shown to be iron, 33% nickel and therefore accurately as        pre-selected.    -   b) Right cylindrical green bodies were then made using the same        procedures as given in Example 2.    -   c) Each of the encapsulated green bodies was then subjected to        high pressure and high temperature conditions in order to cause        diamond particle to particle bonding via partial diamond        recrystallisation. The pressure, temperature, time cycle was        identical to that of Example 2 and 4.    -   d) SEM image analysis was carried out and showed a well sintered        continuous network of diamond, with homogeneity of diamond and        metal alloy. There was an absence of other material phases such        oxides and carbides, in particular, indicating the presence of        only iron nickel alloy metal. The SEM images showing fields of        about 100×120 micro meters taken from various parts of polished        cross sections were identical in regard to the distribution of        diamond and metal. This indicated that above this scale, the        material was homogeneous and could be considered to be        macroscopically stress free.

A finite element method was used in order to numerically assess themicro residual stress magnitude for this composition of PCD material. Itis known from the literature (ref. 4) that iron 33% nickel with 0.6%carbon in solid solution is a low thermal expansion alloy which exhibitsa linear coefficient of thermal expansion of 3.3 ppm ° K⁻¹ at and nearroom temperature which falls within the range of less than 5 ppm ° K⁻¹.The difference in thermal expansion coefficient between diamond and thisalloy was therefore small. The literature elastic modulus for this alloyis about 150 GPa. However, the difference in elastic modulus betweendiamond and this alloy remains high and is typical of transition alloys.During the pressure and temperature release, at the end of themanufacturing cycle, it would therefore be expected that the residualstress would predominantly originate from the differential expansion ofthe metal relative to diamond on pressure release. The micro residualstress in the metal would then be compressive in nature. The calculatedmicro residual principal compressive stress magnitude in the metallicnetwork using the Finite Element analysis with its attendant assumptionswas in excess of −2000 MPa. This Finite Element analysis clearlyindicates that using certain accurately produced low expansion alloysthat the micro residual stress can be compressive. This is an aspect ofthe present invention.

Example 6

PCD free standing, macro residual stress free, bodies were made with thesame diamond composition and size distribution as in Examples 2, 4 and5. The metallic network was pre-selected independently to be 9 volumepercent of the PCD, and to be a cobalt, tungsten carbide cermet. Thiscermet itself was pre-selected to be made up of 78 volume percent cobaltand 22 volume percent tungsten carbide (66.8 weight percent cobalt, 33.2weight percent tungsten carbide).

As in Examples 2, 4 and 5, the method as outlined in FIG. 5 column 2 wasused. The following sequential steps and procedures were carried out inorder to so manufacture this PCD free standing body. The precursorcompounds used were cobalt carbonate and tungstic oxide, WO₃.

-   -   a) 100 g of diamond powder identical to that used in Examples 2,        4 and 5 was suspended in 2.5 litres of de-ionised water. While        continuously stirring the suspension, an aqueous solution of        cobalt nitrate was slowly added. Simultaneously an aqueous        solution of sodium carbonate was slowly added. Cobalt carbonate        was precipitated and decorated the diamond particle surfaces.        While maintaining this decorated diamond powder in suspension,        an aqueous solution of ammonium paratungstate was slowly added.        Simultaneously, dilute nitric acid was added. Tungstic oxide,        WO₃, was precipitated and decorated the diamond particle        surfaces. In this way, the diamond surfaces were co-decorated in        both cobalt carbonate and tungstic oxide. The cobalt nitrate        solution was made by adding 96.3 g of cobalt nitrate hexahydrate        crystals, Co(NO₃)₂.6H₂O to 200 ml of de-ionised water. The        sodium carbonate solution was made by adding 35.5 g of pure        anhydrous sodium carbonate, Na₂CO₃, to 200 ml of de-ionised        water. The ammonium paratungstate solution was made by adding        12.9 g of ammonium paratungstate pentahydrate,        (NH₄)₁₀(W₁₂O₄₁).5H₂O to 200 ml of de-ionised water. The dilute        nitric acid solution was made by adding AR grade concentrated        nitric acid to 200 ml of de-ionised water to provide a        concentration of 0.25 mols per litre. The particulate diamond        mass was then washed free of the sodium and ammonium nitrate        by-product of the reaction and any un-reacted soluble material        by several cycles of settling, addition of pure de-ionised water        and decantation. Finally, the diamond particulate mass,        co-decorated in cobalt carbonate and tungstic oxide was dried        under vacuum at 60° C. The dried powder was then placed in an        alumina ceramic boat with a loose powder depth of about 5 mm and        heated in a flowing stream of argon gas containing 5% hydrogen.        The top temperature of the furnace was 1000° C. which was        maintained for 2 hours before cooling to room temperature. This        furnace treatment dissociated and reduced the cobalt carbonate        precursor to form pure cobalt particles. The tungstic oxide        precursor was reduced and the resultant tungsten reacted with        some of the diamond present to form tungsten carbide. The        surfaces of the diamond particles were in this way now        co-decorated in cobalt and tungsten carbide particles. These        particles were always smaller than the diamond particles and        extremely well and homogeneously distributed.        -   A sample of the particulate mass was heat treated in acid to            dissolve the metallic component and ICP chemical analysis            carried out. The atomic ratio of cobalt to tungsten was            found to be approximately 68% Co, 32% W which is consistent            with the pre-selected choice of cermet composition, namely,            78 volume percent cobalt and 22 volume percent tungsten            carbide.    -   b) Right cylindrical green bodies were then made using the same        procedures as given in Example 2.    -   c) Each of the encapsulated green bodies was then subjected to        high pressure and high temperature conditions in order to cause        diamond particle to particle bonding via partial diamond        recrystallisation. The procedures specified in Example 1 were        used except that the pressure and temperature conditions were        significantly lower, specifically 5.6 GPa and 1400° C. as used        in Example 2. Again, the temperature during the return to room        pressure at the end stage of the manufacturing cycle was        maintained close to about 750° C. This precaution was intended        to mitigate any possible shear stresses being applied during the        end stage of the cycle.    -   d) SEM image analysis was carried out and showed a well sintered        continuous network of diamond, with an interpenetrating cermet        network comprising fine tungsten carbide grains bonded with        cobalt. There was an absence of other material phases such        oxides. The SEM images showing fields of about 100×120 micro        meters taken from various parts of polished cross sections were        identical in regard to the distribution of diamond and cermet        network. This indicated that above this scale, the material was        homogeneous and could be considered to be macroscopically stress        free.        -   A finite element method was used in order to numerically            assess the micro residual stress magnitude for this            composition of PCD material. The linear coefficient of            thermal expansion for the particular cermet network (66.8            weight percent cobalt, 33.2 weight percent carbide) produced            was estimated from the literature values for cobalt and            tungsten carbide to be 10.6 ppm ° K⁻¹. This falls within the            range of 10 to 14 ppm ° K⁻¹. Similarly, the modulus of            elasticity was estimated to be 360 GPa. The calculated micro            residual tensile stress magnitude in the metallic/cermet            network was in the range 1800 to 2200 MPa which is            considered to be in the high range as expected for this            composition of PCD material but, nevertheless, clearly less            than the magnitude calculated for the cobalt case of Example            2.

Example 7

PCD free standing bodies each comprising an intergrown diamond networkand an interpenetrating metallic network were made using a startingdiamond powder with an average particle size of 0.5 micro meters. Themetallic network was pre-selected to be 11 volume percent of the PCDmaterial with the metal independently pre-selected to be a 50% by weightnickel, 50% by weight copper alloy. The PCD body was a right cylinder 13mm in diameter and 8 mm long. The method as outlined in FIG. 5 column 2was used whereby the precursor for the metallic component of the PCDbody was reactively created in a water liquid suspension of startingdiamond particles and was caused to nucleate and grow on the surfaces ofthe starting diamond particles. The following sequential steps andprocedures were carried out in order to so manufacture this PCD freestanding body.

-   -   a) 60 g of diamond powder with an average particle size close to        0.5 micro meters was suspended in 2.0 litres of de-ionised        water. While continuously stirring the suspension, an aqueous        mixed solution of copper nitrate and nickel nitrate was slowly        added. Simultaneously an aqueous solution of sodium carbonate        was slowly added. The mixed copper nitrate, nickel nitrate        solution was made by adding 26 g of anhydrous copper nitrate,        Cu(NO₃)₂, and 40 g of nickel nitrate hexahydrate, Ni(NO₃)₂.6H₂O,        to 200 ml of de-ionised water. The sodium carbonate solution was        made by adding 35 g of pure anhydrous sodium carbonate, Na₂CO₃,        to 200 ml of de-ionised water. A mixed copper, nickel basic        carbonate was precipitated and decorated the diamond particle        surfaces. The 0.5 micro meter powder so decorated with the mixed        alkaline carbonate precursor was then removed from suspension        using a laboratory centrifuge. The material was washed free of        the soluble sodium carbonate by-product by a few cycles of        re-suspension in cold de-ionised water and removal from        suspension by centrifuge. The material was dried under vacuum.        The dried powder was then placed in an alumina ceramic boat with        a loose powder depth of about 3 mm and heated in a flowing        stream of argon gas containing 5% hydrogen. The top temperature        of the furnace was 1000° C. which was maintained for 1 hour        before cooling to room temperature. This furnace treatment        dissociated and reduced the mixed copper, nickel basic carbonate        precursor to form pure 50% copper, 50% nickel alloy particles        decorating the surfaces of the diamond particles.    -   b) The general procedures used in Example 1 to produce        consolidated and encapsulated right cylinder green bodies were        then carried out.    -   c) The general procedures used in Example 1 to subject the green        bodies to a pressure of 7.5 GPa at a temperature of 1950° C. for        1 hour were then carried out.    -   d) SEM image analysis was carried out on polished sections of        the resulting PCD bodies and showed a well sintered continuous        network of diamond, with an interpenetrating network comprising        a single phase copper nickel alloy.

Example 8

The PCD material made in Example 2 based upon a multimodal particle sizeof diamond starting powder and with 9 volume percent cobalt was chosenand free standing PCD bodies of the 3-dimensional shape given in FIG. 14were produced. FIG. 14 shows a 3-dimensional shaped PCD body intendedfor use in general applications. The body was of 45 mm of overalllength. These PCD bodies are intended for use in general applicationswhere rock removal is required, such as cutting elements in rotary rockdrills or road planing heads. The bodies had a cylindrical barrel ofdiameter 25 mm diameter and 25 mm long. The cutting end was designed tohave a sloping rounded chisel shape. The bodies were of 45 mm of overalllength.

-   -   a) A quantity of diamond particulate mass decorated with cobalt        was made using the procedures and material quantities using the        method of FIG. 5 column 2 as described in Example 2,        paragraph (a) above.    -   b) 65 g fractions of the diamond-metal powder mass were then        filled into niobium pre-formed canisters which had been placed        in compaction tooling of the desired geometrical shape. The        diamond, metal powder charge was then compacted using a        cylindrical piston. A second niobium cylindrical canister was        then inserted into the tooling so that its outer surface slid        inside the inner cylindrical wall of the first canister. This        pre-compacted green body was then removed from the compaction        tooling and a tungsten carbide hard metal mandrel inserted into        the open end of the second niobium canister. The free air in the        porosities of the pre-compacts was then evacuated and the        canisters sealed under vacuum using an electron beam welding        system known in the art. The canister assemblies were then        subjected to cold isostatic compaction at a pressure of 200 MPa        to consolidate to a high green density and to eliminate spatial        density variations, and thereafter the mandrels removed. In this        way encapsulated, homogeneous green bodies were produced with        measured densities of about 2.6 g·cm⁻³, which correspond to a        porosity of approximately 35% by volume.    -   c) The encapsulated green bodies were then inserted into        pre-compacted semi-sintered high porosity ceramic components        mirroring their shape. This sub-assembly was in turn inserted        into a cylindrical cavity pre-formed in sodium chloride        components so that the low shear strength sodium chloride        completely surrounded the green body containing sub-assembly.        The green bodies were then subjected to high pressure high        temperature cycles as well known in the art of PCD manufacture        at appropriate conditions to cause sintering of the diamond        particles and the formation of the PCD free standing bodies.        Typical conditions were about 5.7 GPa and about 1400° C.        maintained for 25 minutes. The release of pressure and return to        room temperature was carried out as outlined in Example 1        paragraph (c) above.    -   d) A sample of the sintered free standing PCD bodies was        sectioned and polished and examined using SEM. From comparisons        of images taken from various parts of the sections, it was        observed that well-sintered homogeneous PCD material had been        formed. The 3-dimensional geometry as pre-selected and indicated        in FIG. 14 had been maintained with no significant distortion.        By comparing the dimensions of the green bodies and the final        sintered bodies, the dimensional shrinkage was found to be 12%.        Thus, near-net size and shape behaviour was attained during the        manufacture.

Example 9

PCD free standing, macro residual stress free, bodies each comprising anintergrown diamond network with a mean grain size of close to 10 micrometers with an inter-penetrating metallic network made up of cobalt at 9volume % were manufactured. The PCD bodies were chosen to be large discswith the desired diameter of 100 mm and thickness of 3 mm.

-   -   a) A diamond particulate mass decorated in 9 volume % cobalt        particles was produced using the method of FIG. 5 column 2 and        the procedures, chemical protocol and precursor as specified in        Example 2.    -   b) 95 g fractions of this mass were then formed into disc green        bodies of 106 mm diameter and 4 mm thick. Each green body was        pre-compacted into niobium canisters using simple floating        piston and cylinder tooling. The green bodies were vacuum        degassed and the canisters sealed using electron beam welding.        The dimensions of the green body were measured correcting for        the known wall thicknesses of the canisters and the green body        density was calculated to be 2.7 g·cm⁻³, which corresponds to        approximately 33% porosity by volume.    -   c) Each green body was subjected to a pressure, temperature and        time cycle in a large volume belt type high pressure apparatus        known in the art. The specific conditions employed were        typically 5.6 GPa and 1400° C. maintained for 35 minutes. The        precautionary measured aimed at mitigating distortions as        outlined in Example 1 were employed.    -   d) The resultant free standing green bodies suffered a minimal        axially symmetric distortion whereby the thickness at the centre        was about 1% greater than the chosen 3 mm and the thickness at        the periphery of the disc was about 1% less than the chosen        3 mm. The homogeneity of the diamond-metal particulate mass and        the green body density allows the shrinkage during sintering to        be near uniform. The slight distortion experienced in the PCD        discs results from unavoidable material flow characteristics and        is typical of the high pressure apparatus employed. The        distortion is within the range whereby compensating dimensions        of the green body can be used. This may be done by appropriate        slight changes of mass of the diamond charge and the shape of        the compaction tooling. By a series of empirical trials near-net        size and shape large discs of free standing PCD material can be        achieved. After minimal final shaping and polishing free        standing PCD discs 100.5 mm diameter and 2.95 mm thick were        obtained with a final density of 3.9 g·cm⁻³.        -   Image analysis using SEM procedures confirmed the            homogeneity of the PCD material above a scale of about 100            micro meters.

In summary, there is disclosed in this disclosure a polycrystallinediamond (PCD) construction or body which is free standing in that it isnot attached or bonded, in any manner during any stage of themanufacture of the PCD, to a second body or substrate of a dissimilarmaterial. In particular, a substrate such as tungsten carbide/cobalthard metal commonly used in conventional PCD constructions where thecobalt binder metal is infiltrated into a mass of diamond powder tofacilitate diamond particle-to-particle sintering is excluded.

Manufacturing methods whereby the metals required to enable sintering ofthe diamond particles are homogeneously combined with a pre-selecteddiamond powder of chosen specific size distribution are also described.These may allow both the amount and specific metallurgy of the metals tobe independently pre-selected and chosen such that they are independentof the chosen diamond size and size distribution. Thus, keymanufacturing degrees of freedom such as the diamond grain sizedistribution, the metal content of the PCD material and the atomic andalloy composition of the metal may be chosen and pre-selectedindependent of one another.

The PCD body so formed may comprises a single volume of PCD materialwhich is homogeneous at a macroscopic scale, i.e., above a scale definedfor this invention to be greater than ten times the average diamondgrain size, with the coarsest component of grain size being three timesthe average grain size. The homogeneity at this scale provides for thePCD body to be considered as a spatially invariant material. At thismacroscopic scale the PCD body is therefore stress free, having anabsence of residual stress. Another consequence of not directionallyinfiltrating from a substrate is that the PCD body or construction isdimensionally unrestricted in this regard in any or all orthogonaldirections. The dimensions in any particular direction are restrictedonly by the size of the high pressure apparatus used to manufacture thePCD body. With the high pressure apparatus known in the art thedimensions in any or all of the orthogonal directions may be up to 100mm or more. The PCD body or construction can thus be viewed as a true3-dimensional body of any shape and is not restricted to a layer orplate where one dimension is always of the order of a few millimeters,as is the case for conventional PCD bodies or constructs.

Methods are described where diamond particles are combined with themetals, alloys or metal/metal carbide combinations for PCD materialssuch that the metallic particles, grains or entities are smaller thanthe diamond particles. This may ensure the homogeneity of metal diamonddistribution at a scale greater than the diamond particle or subsequentgrain size maximum. The metals, alloys or metal/metal carbide in themass are the sole source of the molten metal necessary and required tocause the sintering of the diamond particles via partial diamondre-crystallization mechanisms.

One method to create particulate diamond-metal masses involves thecrystallization of the precursor compound or compounds for the desiredmetallic particles from solution where the diamond powder particles arepresent in suspension in the solution. The precursor compound may beformed using any of the crystallization procedures known in the art,such as using reduction of temperature and or removal of solvent byevaporation. After total removal of the solvent, liquid suspensionmedia, a well-mixed intimate combination of the diamond powder andprecursor compound or compounds for the metal particles is produced.This method uses precursor compounds which are soluble in the liquidsuspension media. Examples of liquid media or solvents are water andalcohol. Examples of possible precursor compounds are ionic salts,particularly the nitrates of the transition metals. In turn, theprecursor compounds are dissociated and reduced to form the metallicparticles by a heat treatment preferably in a reducing furnaceenvironment.

Another method, as shown in FIG. 5 column 2, concerns the chemicalreactive generation of the desired precursors for the desired metallicparticles in liquid media with the presence of the diamond powders insuspension. Such precursors are significantly insoluble in thesuspension media. The precursor compounds may nucleate and grow on thediamond particle surfaces to form a particulate decoration of thediamond surfaces with particles or grains of the precursor compounds. Tofacilitate the nucleation of the precursor materials on the diamondsurfaces, the surface chemistry of the diamond particles may bepre-selected and/or deliberately altered to be hydrophilic and dominatedby oxygen species prior to the suspension decoration with the precursorcompounds.

In turn, the precursor compounds are dissociated and reduced by a heattreatment, for example in a reducing furnace environment, to formmetallic particles which decorate the diamond particle surfaces and donot form a continuous metallic coat. The furnace environment may be avacuum or involve flowing gas mixtures containing at least one gascapable of reducing the precursors or its dissociative products to themetallic state and/or metal carbide. Typical reductive gases arehydrogen and carbon monoxide. The heat treatment conditions may bepre-selected to be sufficiently high in temperature and of asufficiently long duration to cause controlled amounts of amorphousnon-diamond carbon to be formed on the metal and diamond surfaces.Alternatively, the heat treatment conditions may be pre-selected to besufficiently low in temperature and short in time for non-diamond carbonnot to form at a detectable level. For example when cobalt is used asthe PCD metal component, temperatures above 800° C. for times of an houror more are typical of the former case. The presence or absence ofamorphous non-diamond carbon together with the control of its amount inthe diamond/metal particulate mass is a degree of freedom which may playa role in the sintering mechanisms of the diamond particles.

The metallic particles now decorate the diamond particle surfaces. Thisapproach may assist in ensuring that the metallic particles are alwayssmaller than the diamond particles. Examples of liquid media may includewater and alcohols. Some precursors may be insoluble salts of thetransition metals such as carbonates, oxalates, acetates, tungstates,tantalates, titanates, molybdates, niobates, and the like. The reactantsto reactively form these precursors are soluble salts in the chosensolvent or suspension medium. A reactant source of transition metalssuch as iron, nickel, cobalt, manganese, chromium, copper and the likemay be nitrate salts. Alternatively, precursor compounds for transitionmetals which form stable carbides such as tungsten, molybdenum,tantalum, titanium, niobium, zirconium and the like may be oxidesgenerated by the reaction of alkoxide compounds with water in alcoholsuspension media. A reaction to generate tungstic oxide, WO₃ as aprecursor to form tungsten carbide on diamond particle surfaces may bethe reaction of ammonium paratungstate with dilute mineral acids such asnitric acid in water as solvent and suspension medium for the diamond.

Any of these chemical reactions to form the precursor compound decorantson the diamond particle surfaces may be done in sequence and applied tothe pre-selected diamond powder as a whole or to any component of thediamond powder in appropriate suspension media. The diamond powdercomponents may be based upon mass fractions or upon size, sizedistribution or any desired combination of these. Some of the diamondpowder components may be left undecorated.

The above described methods of preparing the diamond grains andprecursors assist in achieving high homogeneity in the sinteredproducts.

Diamond powder fractions or components may also differ in diamond type,based upon the lattice defect composition and structure of the diamondcrystals. A convenient way of such differentiation of diamond typebetween the diamond powder fractions or components can be to use diamondof natural origin as opposed to standard synthetic diamond origin. Thelattice defects in natural diamonds are typically and predominantly madeup of aggregated nitrogen impurity atomic structures. In contrast, thelattice defects in typical synthetic diamonds commercially crystallizedusing molten transition metal solvents are overwhelmingly dominated bysingle nitrogen atoms which substitute for individual carbon atoms.Moreover, the overall nitrogen content in natural diamond is typicallyan order of magnitude greater than for such synthetic diamond. PCDmaterials made with these different types of diamond exhibitsignificantly different properties. Pre-selected combinations of naturaland synthetic diamonds may also be used for purpose.

In turn, the precursor compounds are dissociated and reduced to formmetallic particles by a heat treatment, for example in a reducingfurnace environment. In this way, different components of the diamondpowder may be decorated in any of the different metallic particles andto any different degree. Thus the metallic particles may be pre-selectedboth in elemental composition and amount to be associated and decoratedonto any chosen sub-component of the diamond particles. A vast number ofPCD free standing body embodiments with desired compositions, structuresand properties may, in this way, be generated using such prepareddecorated diamond powder, metal combinations or masses.

The methods involving liquid suspension procedures may have particularutility in that they may be easily altered in scale and may allowproduction quantities of kilograms or more of accurate, homogeneouscombinations of the diamond and metals and metals/metal carbides to bemade. Moreover a notable and valuable characteristic of one method isthat wide ranging combinations of diamond particles and metals, whichmay be pre-selected to vary independently in diamond particle size,metal amount and metal elemental composition, may be made.

The masses of diamond particle, metal combinations generated by theabove methods are consolidated into cohesive so called “green bodies” ofa pre-selected size and 3-dimensional shape. Consolidation may beeffected in compaction die arrangements or isostatic compactionapparatuses as known in the art. Preferably hot isostatic compaction maybe employed. Isostatic compaction techniques may have the benefit ofspatial homogeneity of density in the green body, which assists inensuring that the homogeneity of the starting diamond powder, metalcombination is maintained and in turn engenders directionally equalshrinkage during subsequent sintering of the diamond particles. Freestanding PCD bodies of near net pre-determined shape may then be made.The degree of shrinkage on sintering to form the PCD body may bemeasured for each specific diamond and metal composition. Such knowledgeallows the size of resultant PCD body to be preselected for each PCDcomposition. Free standing PCD bodies of near net pre-determined sizemay then be made.

Temporary organic binders may be employed to provide cohesion in thegreen bodies. A special case of this and as an alternative to isostaticcompaction, gel casting techniques may be employed as known in the art.This technique to form the green bodies also maintains spatialhomogeneity of the diamond and metal distributions so that directionallyequal shrinkage on sintering may occur, so that the 3-dimensional shapeof the green body may be maintained on formation of the free standingbody. There is a large number of powder, slurry and suspension basedconsolidation and green body formation techniques known in the art formaterial fabrication from particulate starting materials. In addition tothose already disclosed above, these include injection moulding, slipcasting, electrophoresis enhanced sedimentation, centrifugal enhancedsedimentation, 3-dimensional printing and many others. Each of theconsolidation and green body making techniques has it own character inregard to the size of particles it may viably be applied to and also thedegree to which homogeneity including that of porosity can bemaintained. Preferences of techniques to be applied to make any given3-dimensional and material embodiments take such character of thetechnique into consideration. In particular, the ability of a techniqueto be accurate, reproducible and maintain spatial homogeneity all inregard to porosity is of importance in the choice of preferredtechniques to be used for any particular embodiment. This considerationis directed at the achievement of near net size and shape.

The green bodies generated by the above methods are subjected to highpressure, high temperature conditions for appropriate times to causesintering of the diamond particles and form the free standing PCDbodies. Typical pressure and temperature conditions are in the range of5 to 15 GPa and in the range of 1200 to 2500° C. respectively.Preferably pressures in the range 5.5 to 8.0 GPa along with temperaturesin the range 1350 to 2200° C. may be used.

There is also disclosed a means of managing and controlling the microresidual stress magnitude of the free standing macro residual stressfree PCD body, i.e., below a scale defined to be less than ten times theaverage grain size, where the coarsest component of grain size is nogreater than three times the average grain size. Above this scale someembodiments provide for the PCD free standing body to be residual stressfree, i.e., macro residual stress free. The methods disclosed may allowa very wide range of diamond to metal ratios and accurate metalcompositions to be pre-selected independently of resultant diamond grainsize and size distribution. Thus the relative differences inthermo-elastic properties between the diamond network and that of themetallic network can be pre-selected and accurately controlled.

Often, but not exclusively, the dominant properties in this regard arethe thermal expansion coefficients of the metals in comparison to thatof diamond. In such cases, on return to ambient conditions oftemperature and pressure during the manufacturing process the relativedifferences of properties cause the diamond network to be generallycompressed and the metallic network generally put into a state oftension. For each PCD body material pre-selected in regard to diamondand overall metal content, the micro residual stress magnitudes may thusbe considered to be high, medium or low in magnitude by the use of metalcompositions with thermal expansion coefficients in the ranges of 10 to14, 5 to 10 and less than 5 ppm ° K⁻¹, respectively.

Some embodiments include the high carbon versions of controlledexpansion transition metal alloys. A notable low expansion alloy with avery low minimum of linear coefficient of thermal expansion is an iron,33 weight % nickel, 0.6 weight % carbon alloy (ref. 4). This alloy has aliterature linear coefficient of thermal expansion value of 3.3 ppm °K⁻¹, which falls into the less than 5 ppm ° K⁻¹ category. This alloywould then be expected to provide a metallic network in PCD materialswhere the tensile residual stress magnitude in the metallic network islow. However, this alloy has an elastic modulus of approximately 200GPa, which is very different and removed from the elastic modulus of thediamond network, typically 1050 GPa. In such a case, the elasticproperty difference should dominate when the manufacturing conditionsare returned to room conditions. The differential expansion of thediamond and metallic networks on release of pressure should then resultin the metallic network experiencing a compressive micro residualstress. Thus, where metals of low thermal expansion coefficients areused it is possible that the residual stress in the metallic network canbecome compressive.

Any or all of the above aspects may provide for the manufacture of freestanding PCD bodies, not attached to a dissimilar material, comprising apre-selected combination of intergrown diamond grains of specific sizeand size distribution, in conjunction with an independently pre-selectedspecific metallic inter-penetrating network, with an independentlypre-selected specific overall metal to diamond ratio. These primarydegrees of freedom may be independently pre-selected.

Some embodiments may benefit from removal of the metal from a chosendepth from the surface of the PCD body or throughout the volume of thePCD body. This may be done using, for example, chemical leachingtechniques well known in the art.

In summary, embodiment methods involve, for example, diamond particlesuspension in a liquid and the crystallisation and/or precipitation ofprecursor compound for the required metals of the PCD material to beformed and the subsequent thermal decomposition/reduction of theseprecursors to form the metals. These methods are inherentlycharacterised by the resultant metallic particles being smaller than thechosen diamond particles. The described methods involving diamondparticle suspensions and the crystallisation and/or precipitation ofprecursor compounds for the metals become more and more practicable andefficient as the diamond particle sizes become smaller and smaller downto and including sub-micron sizes. This is due to the precursorcompounds for the metals being influenced in their crystallisationand/or precipitation by the overall diamond surface area, which becomesprogressively larger as the diamond particles become smaller. Inaddition, dissociation/reduction of precursor compounds for metalsreadily form very fine and often nano-sized metal particles. The methodsdescribed herein for forming embodiments of free standing bodies of PCDmaterial thus provide good practicality for PCD materials with desiredvery fine diamond grain sizes, particularly for diamond grain sizes inthe sub-micron range.

This character of these suspension methods, along with the suspensionstirring dynamics, provides for a high degree of homogeneity of mix ofthe diamond particles and metallic particles, and may even approach theultimate homogeneity in this regard. This homogeneity of diamond andmetal in a particulate mass assists in the formation of a green body andsubsequent free standing PCD body formed at high pressure hightemperature which is homogeneous with respect to its diamond andmetallic composition above a scale related to the average and maximumgrain size of the diamond grain size of the diamond network and alsowhich spans the dimensions of the free standing PCD body. This scale canbe used to define the so-called “macroscopic” scale of the PCD material.It has been experientially determined by the inventors that using themethods described herein the diamond network to metallic network volumeratio is spatially constant and invariant above a scale greater than tentimes the average diamond grain size, provided that the largestcomponent of diamond grain size is no greater than three times theaverage diamond grain size. This spatial invariance of diamond networkto metallic network volume ratio at the defined macroscopic scale,across the dimensional span of the PCD body means that, at completion ofthe manufacturing process, the free standing PCD body will bemacroscopically residual stress free.

Conversely, if the PCD body is inhomogeneous, with the diamond networkto metallic network volume ratio varying from place to place in the PCDbody, the PCD material from place to place will differ in thermalexpansion and elastic properties. These spatial differences inproperties then necessarily lead to a significant macroscopic residualstress field across the dimensional span of the PCD body, caused by thespatial differential in contraction, when the PCD body is returned toroom temperature and pressure at the end of the high temperature highpressure process.

Free standing PCD bodies of embodiments which are residual stress freemay have considerable benefits in applications involving mechanicalaction such as general machining, drilling and the like. In suchapplications, the tooling material efficiency is often governed by crackrelated processes leading to undesired fracture behaviour such aschipping and spalling. It is well known in the art that macroscopic,tool piece dimension spanning, residual stress fields can easily enhancethe propagation of cracks and thereby increase the occurrence ofchipping and spalling. The absence of macroscopic residual stress fieldsmitigates such behaviour and such absence is therefore desirable.

REFERENCES

-   1. D. Dollimore, “The thermal decomposition of oxalates. A review”,    Thermochimica Acta, 117 (1987), 331-363.-   2. C. Ehrhardt, M. Gjikaj, W. Brockner, “Thermal decomposition of    cobalt nitrate compounds: Preparation of anhydrous cobalt (II)    nitrate and its characterization by Infrared and Raman spectra”,    Thermochimica Acta, 432 (2005), 36-40.-   3. W. Brockner, C. Ehrhart, M. Gjikaj, “Thermal decomposition of    nickel nitrate hexahydrate, Ni(NO₃)₂.4H₂O”, Thermochimica Acta, 456    (2007), 64-68.-   4. E. L. Frantz, “Low-Expansion Alloys”, Metals Handbook, 10^(th)    ed, vol. 2, 889-896.-   5. Chien-Min Sung, “A Century of Progress in the Development of Very    High Pressure Apparatus for Scientific Research and Diamond    Synthesis”, High Temperatures-High Pressures, Vol. 29, p 253-293.    (1997).

1. A method of producing a free standing PCD body comprising acombination of intergrown diamond grains forming a diamond network andan interpenetrating metallic network, not attached to a second body orsubstrate made of a different material such as a metal, cermet orceramic, the method comprising the steps of: a. forming a mass ofcombined diamond particles and precursor compound(s) for the metals ofthe metallic network by suspending the diamond particles in a liquid,and crystallising and/or precipitating the precursor compounds in theliquid; b. removing the mass from suspension by sedimentation and/orevaporation to form a dry powder of combined diamond particles andprecursor compound(s); c. subjecting the powder to a heat treatment todissociate and reduce the precursor compound(s) to form metal particlessmaller in size than the diamond particles to provide a homogeneousmass; d. consolidating the homogeneous mass of diamond particles andmetallic material using isostatic compaction to form a homogeneouscohesive green body of a pre-selected size and 3-dimensional shape; ande. subjecting the green body to high pressure and high temperatureconditions such that the metallic material wholly or in part becomesmolten and facilitates diamond particle to particle bonding via partialdiamond re-crystallisation to form a free standing PCD body; wherein:the diamond network of the PCD body is formed of diamond grains having aplurality of grain sizes, the diamond network comprising a grain sizedistribution having an average diamond grain size, wherein the largestcomponent of the diamond grain size distribution is no greater thanthree times the average diamond grain size; and the PCD material formingthe free standing PCD body is homogeneous, the PCD body being spatiallyconstant and invariant with respect to diamond network to metallicnetwork volume ratio, wherein the homogeneity is measured at a scalegreater than ten times the average grain size and spans the dimension ofthe PCD body, the PCD material being macroscopically residual stressfree at said scale.
 2. A method according to claim 1 wherein the mass ofcombined diamond particles and precursor compound(s) for the metals ofthe metallic network is formed by simultaneously or sequentially addingto the suspension a solution of a metal containing compound and asolution of a reactive compound such that an insoluble precursorcompound(s) for the metal(s) of the metallic network nucleates and growson the surfaces of the diamond particles forming the precursorcompound(s) as particles attached to and decorating the diamond particlesurfaces.
 3. A method according to claim 1 wherein the mass of combineddiamond particles and precursor compound(s) for the metals of themetallic network is formed by crystallizing from solution in thesuspending liquid a soluble precursor compound(s) for the metals of themetallic network.
 4. A method according to claim 2 wherein the precursorcompound(s) for the metal of the metallic network is (are) crystallizedand/or precipitated in a suspension of pre-selected portion of thediamond particles; the method further comprising after completion of thecrystallization and/or precipitation of the precursor compound(s) addingthe remaining portion of the diamond particles to the stirred suspensionprior to removal of the suspension liquid; and subsequently applyingheat treatment to dissociate and/or reduce the precursor compound(s) tometallic particles.
 5. A method according to claim 4 wherein the portionof diamond particles for initial combination with the precursorcompound(s) is pre-selected on the basis of diamond particle size and/ordiamond mass proportion. 6-8. (canceled)
 9. A method according to claim1, wherein the liquid suspension medium is water or an alcohol. 10.(canceled)
 11. A method according to claim 2, wherein the precursorcompound(s) is (are) a carbonate, hydroxide, oxalate or acetate.
 12. Amethod according to claim 3, wherein the precursor compound(s) is anitrate. 13-15. (canceled)
 16. A method according to claim 2, whereinthe precursor compound(s) is (are) selected from tungstates, molybdates,tantalates, titanates, niobates, vanadates and stannates. 17-18.(canceled)
 19. A method according to claim 2 wherein the precursor is anamorphous semi-porous oxide.
 20. A method according to claim 19 whereinthe oxide is selected to be any one or more of or any permutation oftungstic oxide, WO₃, molybdic oxide, MoO₃, tantalum pentoxide, Ta₂O₅,titanium oxide, TiO₂, niobium pentoxide, Nb₂O₅, and vanadium oxide,V₂O₃.
 21. A method according to claim 20 wherein the reactant compoundto form the oxide by reaction with water is an alcoxide of generalformula M(ROH)_(n), M being a metal and R being an organic alkane.
 22. Amethod according to claim 2, wherein the mass of diamond particles andprecursor compound(s) is heated in a reducing gas environment to convertthe precursor compound(s) to metallic particles smaller than the diamondparticles.
 23. A method according to claim 22 wherein the gaseousenvironment contains hydrogen.
 24. A method according to claim 22,wherein the temperature and time of heat treatment is sufficient togenerate amorphous non-diamond carbon where metallic particles decorateand are attached to the diamond surfaces and/or are in contact with thediamond surfaces.
 25. A method according to claim 22, wherein thetemperature and time of heat treatment is insufficient to generateamorphous non-diamond carbon where metallic particles decorate and areattached to the diamond surfaces and/or are in contact with the diamondsurfaces.
 26. A method according to claim 2, wherein one or more of theprecursor compound(s) yields one or more transition metal carbides atthe surface of the diamond particles during heat treatment.
 27. A methodaccording to claim 26 wherein the precursor compound(s) yield ametal/metal carbide combination attached to the diamond surfaces.
 28. Amethod according to claim 27 where the metal/metal carbide combinationis selected from cobalt/tungsten carbide, cobalt/tantalum carbide ornickel/titanium carbide or any combination.
 29. A method according toclaim 1 wherein the green body is subjected to a pressure in the rangeof 5 to 10 GPa and to a temperature in the range 1100 to 2500° C. toform a fully dense free standing PCD body. 30-31. (canceled)